The world of the jinn is an independent and separate world with its own distinct nature and features that are hidden from the world of humans. Jinns and humans have things in common, such as the ability to understand and choose between good and evil. The word jinn comes from the Arabic root meaning “hidden from sight”.
Allah has told us in His Book the essence from which the jinn were created. He says: “And the jinn, We created aforetime from the smokeless flame o fire.” (Al-Hijr : 27)
“O assembly of jinns and mankind! Did there not come to you Messengers from amongst you, reciting unto you My Aayaath…?” [al-An’aam 6:130]
A’ishah (may Allah be pleased with her) says that the Prophet (peace and blessings be upon him) said: “The angels were created from light, the jinn were created from fire, and Adam was created from that which has been described to you.” Muslim, 5314
Allah has created different types of jinn. Among them are some who can take on different forms, such as dogs and snakes; some who are like flying winds with wings; and some who can travel and rest. Abu Tha’labah al-Khushani said: “The Messenger of Allah (peace and blessings of Allaah be upon him) said: ‘The jinn are of three types: a types that has wings, and they fly through the air; a type that looks like snakes and dogs; and a type that stops for a rest then resumes its journey.” (Reported by al-Tahhaawi in Mushkil al-Athaar, 4/95, and by al-Tabaraani in al-Kabeer, 22/214. Shaykh al-Albaani said in al-Mishkaat (2/1206, no. 4148): al-Tahhaawi and Abu’l-Shaykh reported it with a saheeh isnaad).
Every individual among the sons of Aadam has a jinn who has been appointed to be his constant companion (qareen). Ibn Mas’ood said: “The Messenger of Allaah (peace and blessings of Allah be upon him) said, ‘There is not one of you who does not have a jinn appointed to be his constant companion.’ They said, ‘And you too, O Messenger of Allaah?’ He said, ‘Me too, but Allaah has helped me and he has submitted, so that he only helps me to do good.’” (Reported by Muslim, 2814). Al-Nawawi said in his commentary on Muslim (17/175): “‘He has submitted’ … he became a believing Muslim. This is the apparent meaning. Al-Qaadi said: Know that the ummah is agreed upon the fact that the Prophet (peace and blessings of Allaah be upon him) was protected from Shaytaan, physically and mentally, and with regard to his speech. This hadeeth contains a reference to the warning against the fitnah (temptation, trial) and whispers of the qareen (constant companion from among the jinn). We know that he is with us so we should beware of him as much as possible.”
Allaah has given the jinn powers that he has not given to humans. Allaah has told us about some of their powers, such as the ability to move and travel quickly. An ‘ifreet from among the jinn guaranteed to the Prophet Sulaymaan (peace be upon him) that he would bring the throne of the Queen of Yemen to Jerusalem in a moment faster than that needed for a man to get up from where he was sitting. Allaah says (interpretation of the meaning):
“An ‘ifreet (strong one) from the jinns said: ‘I will bring it [her throne] to you before you rise from your place (council). And verily, I am indeed strong, and trustworthy for such work.’ One with whom was knowledge of the Scripture said: ‘I will bring it to you within the twinkling of an eye!’ – then when Sulaymaan saw it placed before him, he said, ‘This is by the Grace of my Lord…’” [al-Naml 27:39-40].
The jinn eat and drink. Ibn Mas’ood said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘Someone from among the jinn called me, and I went with him and recited Qur’aan for them.’ He took us and showed us the traces of where they had been and the traces of their fires. They asked him for food and he said, ‘You can have every bone on which the name of Allaah has been mentioned that comes into your possession, as meat, and all the droppings as food for your animals.’ The Prophet (peace and blessings of Allaah be upon him) said, ‘So do not use [these things] for cleaning yourselves [after relieving oneself], for they are the food and provision of your brothers.’” (Reported by Muslim, 450). According to another report: “A delegation of jinn from Island(Jazera) came to me, and what good jinn they are! They asked me for food and He said: 'Every bone upon which Allah's name has not been mentioned, that falls into your hands, and every dropping of dung is fodder for your beasts..” Tirmidhi Vol. 5, Book 44, Hadith 3258. The believing jinn may eat any bone on which the name of Allaah has been mentioned, because the Messenger (peace and blessings of Allaah be upon him) did not permit them to have anything on which Allaah’s name has not been mentioned – those are for the kuffaar among the jinn.
According to the hadeeth narrated by Ibn Mas’ood, that we have quoted above, the jinn asked the Messenger (peace and blessings of Allaah be upon him) for provision, and he said to them: “…and [you can have] all the droppings as food for your animals.”
The jinn live on this earth where we do. They are mostly to be found in ruins and unclean places like bathrooms, dunghills, garbage dumps and graveyards. Hence the Prophet (peace and blessings of Allaah be upon him) taught us to take precautions when entering such places, by reciting the adhkaar (prayers) prescribed by Islam. One of these was reported by Anas ibn Maalik (may Allaah be pleased with him), who said: “When the Messenger of Allaah (peace and blessings of Allaah be upon him) entered the toilet, he would say, ‘Allaahumma innee a’oodhu bika min al-khubuthi wa’l-khabaa’ith (O Allaah, I seek refuge with You from the evil ones, male and female).’” (Reported by al-Bukhaari, 142; and Muslim, 375). Al-Khattaabi explained that khubuth is the plural of khabeeth (evil or dirty – masculine form), and khabaa’ith is the plural of khabeethah (evil or dirty – feminine form), and that what is meant is male and female shayaateen.
Allaah tells us that some of the jinn said (interpretation of the meaning):
“ ‘And some of us are Muslims, and of us some are al-qaasitoon (disbelievers – those who have deviated from the Right Path). And whosoever has embraced Islam, then such have sought the Right Path. And as for the qaasitoon, they shall be firewood for Hell.’” [al-Jinn 72:14-15]
The Muslims among the jinn are of different levels as regards righteousness and taqwa. Allaah says (interpretation of the meaning):
Narrated by 'Aisha ®: Some people asked Allah's Apostle (May Allah honour Him and Grant Him peace) about the foretellers. He said. -They are nothing." They said, -O Allah's Apostle! Sometimes they tell us of a thing which turns out to be true." Allah's Apostle said, "A Jinn snatches that true word and pours it into the ear of his friend (the foreteller) (as one puts something into a bottle). The foreteller then mixes with that word one hundred lies." Sahih Al Bukhari Vol 7:657
Thus, it is clear from this as to how fortune-tellers get predictions of the future right. It is also evident as to why they get so many wrong. Men like Nostradamus (Michel de Nostradamus was a famous French soothsayer of the 16th century.) are an example, as some of his predictions of the future were correct whilst many were completely wrong. Unfortunately, the amount of fortune telling which occurs amongst the Muslims is also increasing. By visiting Muslim lands such as Morocco, one is able to see as to how much inter Jinn-fortune-teller activity there really is. If you look up at the sky on a clear night in Morocco, you will see the heavens ablaze with shooting stars! A clear display of the devils being chased away from the heavens.
Fortune-tellers also operate through the Qareen. The Qareen is the Jinn companion which is assigned to every human being. It is this Jinn which whispers to our base desires and constantly tries to divert us from righteousness. The Prophet (saws) said: "Everyone of you has been assigned a companion from the Jinn. The companions asked: Even you O' Messenger of Allah? And the Prophet replied: Even me, except that Allah has helped me against him and he has submitted. Now he only tells me to do good" (Muslim - Eng. Trans. Vol.4, p.1472, No.6757). Because the Qareen is with a person all his life, it knows all that has happened to the person from the cradle to the grave. By making contact with the Qareen, the fortune-teller is thus able to make out that it is he who knows about the person. He looks in his crystal ball or the palm of a person and proceeds to amaze him with knowledge which no one else knows. The severity of going to a fortune-teller is such that the Prophet (saws) said: "The prayer of one who approaches a fortune-teller and asks him about anything, will not be accepted for forty days or nights" (Muslim - Eng. Trans. Vol.4, p.1211, No.5540) and: "Whosoever approaches a fortune-teller and believes in what he says, has disbelieved in what was revealed to Muhammed" Reported by Ahmed 
Because the jinn can see us while we cannot see them, the Prophet (peace and blessings of Allaah be upon him) taught us many ways to protect ourselves from their harm, such as seeking refuge with Allaah from the accursed Shaytaan, reciting Soorat al-Falaq and Soorat al-Naas (the last two Soorahs of the Qur’aan), and reciting the words taught by Allaah in the Qur’aan (interpretation of the meaning): “Say: ‘My Lord! I seek refuge with You from the whisperings (suggestions) of the shayaateen (devils). And I seek refuge with You, my Lord, lest they may attend (or come near) me.’” [al-Mu’minoon 23:97-98]
Saying Bismillaah (in the Name of Allaah) before entering one’s home, before eating or drinking, and before having intercourse will also keep the Shaytaan from entering the house or partaking with a person in his food, drink and sexual activity. Similarly, mentioning the name of Allaah before entering the toilet or taking off one’s clothes will prevent the jinn from seeing a person’s ‘awrah or harming him, as the Prophet (peace and blessings of Allaah be upon him) said, “To put a barrier that will prevent the jinn from seeing the ‘awrah of the sons of Aadam, let any one of you say ‘Bismillaah’ when entering the toilet.” (Reported by al-Tirmidhi, 551; Saheeh al-Jaami’, 3611).
Strength of faith and religion in general will also prevent the jinn from harming a person, so much so that if they were to fight, the one who has faith would win. ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased with him) said: “A man from among the Companions of Muhammad met a man from among the jinn. They wrestled, and the human knocked down the jinn. The human said to him, ‘You look small and skinny to me, and your forearms look like the front paws of a dog. Do all the jinn look like this, or only you?’ He said, ‘No, by Allaah, among them I am strong, but let us wrestle again, and if you defeat me I will teach you something that will do you good.’ The human said, ‘Fine.’ He said, ‘Recite, ‘Allaah! None has the right to be worshipped but He, the Ever-living, the One Who sustains and protects all that exists…’ [Aayat al-Kursi – al-Baqarah 2:255 – interpretation of the meaning]. The human said, ‘Fine.’ He said, ‘You will never recite this in your house but the Shaytaan will come out of it like a donkey breaking wind, and he will never come back in until the next morning.’” (Reported by al-Daarimi, 3247).
It was narrated that Abu Hurayrah said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) put me in charge of guarding the zakaah of Ramadaan. Someone came to me and started grabbing handfuls of the food. I took hold of him and said, ‘I will take you to the Messenger of Allaah (peace and blessings of Allaah be upon him).’ He said, ‘I will teach you some words by means of which Allaah will benefit you.’ I said, ‘What are they?’ He said, ‘When you go to your bed, recite this aayah (interpretation of the meaning): “Allaah! Laa ilaaha illa Huwa (none has the right to be worshipped but He), Al-Hayyul-Qayyoom (the Ever Living, the One Who sustains and protects all that exists)…” [al-Baqarah 2:255] – until he completed the aayah. Then Allaah will appoint a guard for you who will stay with you and no shaytaan (devil) will come near you until morning.’ The Messenger of Allaah (peace and blessings of Allaah be upon him) asked me, ‘What did your prisoner do last night?’ I said, ‘O Messenger of Allaah, he taught me something, and claimed that Allaah would benefit me by it.’ He said, ‘What was it?’ I said, ‘He taught me to recite Aayat al-Kursiy when I go to bed, and said that no shaytaan would come near me until morning, and that Allaah would appoint a guard for me who would stay with me.’ The Prophet (peace and blessings of Allaah be upon him) said, ‘He told you the truth, although he is an inveterate liar. That was the Shaytaan.’ (Narrated by al-Bukhaari, 3101) 
It was narrated from Sulaymaan ibn Sard that two men were trading insults in the presence of the Prophet (peace and blessings of Allaah be upon them), until the face of one of them turned red. The Prophet (peace and blessings of Allaah be upon him) said, “I know a word which, if he were to say it, what he is suffering from would go away: ‘A’oodhu Billaahi min al-Shaytaan il-rajeem (I seek refuge with Allaah from the accursed Shaytaan).’” (Narrated by al-Bukhaari, 3108; Muslim, 2610)
Reciting al-Mi’wadhatayn (the last two Soorahs of the Qur’aan, al-Falaq and al-Naas). It was narrated that Abu Sa’eed al-Khudri (may Allaah be pleased with him) said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) used to seek refuge with Allaah from the jinn and from the evil eye until the Mi’wadhatayn were revealed, and when they were revealed he started to recite them and not anything else.”
It was narrated from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Do not make your houses like graves, for the Shaytaan runs away from a house in which Soorat al-Baqarah is recited.”(Narrated by Muslim, 780)
It was narrated that Abu Mas’ood al-Ansaari said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘Whoever recites the last two Aayaath of Soorat al-Baqarah at night, that will suffice him.’” (Narrated by al-Bukhaari, 4723; Muslim, 807). It was narrated from al-Nu’maan ibn Basheer (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “Allah inscribed a book two thousand years before He created the heavens and the earth, from which the last two aayahs of Soorat al-Baqarah were revealed. If they are recited for three nights, no shaytaan (devil)will remain in the house).
It was narrated from al-Haarith al-Ash’ari that the Prophet (peace and blessings of Allah be upon him) said: “Allah commanded Yahyaa ibn Zakariyah (peace be upon him) five things to follow and to enjoin upon the Children of Israel… and he commanded them to remember Allaa, and the likeness of that is a man who was being pursued by the enemy, until he reached a strong fortress in which he found protection; similarly a man cannot find protection from the Shaytaan except by remembering Allaah…” (Narrated by al-Tirmidhi, 2863; he said it is hasan saheeh. The hadeeth was classed as saheeh by al-Albaani in Saheehal-Jaami’,1724)
Reciting “Laa ilaaha ill-Allaah wahdahu laa shareeka lah, lahu’l-mulk wa lahu’l-hamd wa huwa ‘ala kulli shay’in qadeer (There is no god except Allaah Alone with no partner or associate; His is the Sovereignty and His is the praise, and He is Able to do all things)” one hundred times.
It was narrated from Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever says “Laa ilaaha ill-Allaah wahdahu laa shareeka lah, lahu’l-mulk wa lahu’l-hamd wa huwa ‘ala kulli shay’in qadeer” one hundred times in the day, will have a reward equivalent to that of freeing ten slaves, one hundred hasanahs (good deeds) will be recorded for him, and one hundred sayi’ahs (bad deeds) will be erased from his record, and it will be protection for him from the Shaytaan for that day, until evening comes. No one could achieve any better than him except the one who does more than he did.” (narrated by al-Bukhaari, 31119; Muslim, 2691)
It was narrated that Suhayl ibn Abi Saalih said: “My father sent me to Bani Haarithah, and there was with me a slave of ours, or a companion of ours. Someone called out his name from a garden, and the one who was with me looked into the garden and did not see anything. I mentioned that to my father, and he said, ‘If I had known that this was going to happen to you, I would not have sent you. But if you hear a voice then make the call for prayer, for I heard Abu Hurayrah (may Allaah be pleased with him) narrating that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “When the Shaytaan hears the call to prayer, he runs away fast.”’”(Narrated by Muslim, 389). The word translated here as “runs away fast” may also mean “farting.”
Allah says (interpretation of the meaning): “And when you (Muhammad) recite the Qur’aan, We put between you and those who believe not in the Hereafter, an invisible veil (or screen their hearts, so they hear or understand it not) [al-Israa’ 17:45] 
Shaykh Muhammad bin Saalih al-`Uthaymeen was asked “Is there any proof that supports the claim that jinn can possess human beings?”
Yes, there is proof in the Book and the Sunnah that jinn enter humans. In the Qur'aan, Allaah Almighty Says: Those who eat Riba (usury and interest) will not stand (on the Day of Resurrection) except like the standing of a person beaten by Shaytaan leading him to insanity. Suarh Al Baqarah 2:275
Ibn Kathir, may Allaah have mercy upon him, commented: "They will rise from their graves like a person rises who is possessed by the Shaytaan."
Regarding proof from the Sunnah, the Messenger of Allaah Salallaahu alayhi wasallam said, "Indeed, Shaytaan flows through the son of Adam like the flow of his blood." Sahih Al-Bukhari 2039 and Sahih Muslim 2175
In Manqalat Ahl As-Sunnah wal-Jamma'ah, Al-Ash'ari said that they -meaning Ahl As-Sunnah- say that the jinn enter into the body of the possessed as proven by the preceding verse.
'Abdullaah, Imaam Ahmad's son, said, "I said to my father that a group of people claimed that jinn don't enter into the bodies of human beings. He said, 'O my son, they are lying; don't you see that it is they who are speaking upon their tongues."
In a number of Hadiths from the Messenger of Allaah Salallaahu alayhi wasallaam, recorded by Imaam Ahmad and Al-Bayhaqi, it is reported that he met a boy who was possessed. So the Prophet Salallaahu alayhi wasallaam began saying, "Come out, O enemy of Allaah. Come out, O enemy of Allaah." Sunan Ibn Majah 3548
In some versions he said, Come out, O enemy of Allaah. Come out, O enemy of Allaah."Musnad Ahmad 4/171, 172
Then the boy healed and became normal.
Here we have mentioned one proof from the Qur'aan and two from the Sunnah; what people witness everyday serves as tangible evidence, not to mention that this is the view of Ahl As-Sunnah wal-Jama'ah. Nevertheless, we do not deny that some people are insane due to some other defect in their mind. Fatawa Islamiyah, vol.8, P.322 DARUSSALAM