Dreams are successions of images, ideas, emotions and sensations occurring involuntarily in the mind during certain stages of sleep. The scientific study of dreams is known as Oneirology. Scientists believe that everyone dreams, but people will tend to forget them when they naturally pass out of sleep through the traditional sleep cycle. If a person is awoken during REM sleep, they are much more likely to remember the dream.
Dreams mainly occur in the sleep, that is when brain activity is high and signaled by continuous movements of the eyes. At times, dreams may occur during the other stages of sleep. However, the dreams tend to be much less memorable and less vivid. Dreams can last for a few seconds, or as long as twenty minutes. Dreams are a connection to the human subconscious.
Islamically Dreams are of three kinds, its detail is given below. 
True dreams are a part of Prophethood, as it was reported that the Prophet Muhammad صلى الله عليه و سلم said: “True dreams are one of the forty-six parts of Prophethood.” Sahih Al Bukhaari, 6472; Sahih Muslim, 4201
Dreams marked the onset of Revelation (al-Bukhaari, 3; Muslim, 231). The truthfulness of the dream is related to the sincerity of the dreamer. Those who have the most truthful dreams are those who are the most truthful in speech. Sahih Muslim, 4200
Everything that causes distress to people and upsets them, the shaytaan is eager for it, whether it is when they are awake or asleep, because the shaytaan is an enemy as Allah سبحانه و تعالى says (interpretation of the meaning): “Surely, Shaytaan (Satan) is an enemy to you, so take (treat) him as an enemy” Qur’an.Surah Faatir 35:6
Abu Hurayrah رضي الله عنه, which says that the Prophet Muhammad صلى الله عليه و سلم said: “When the time (of the Day of Resurrection) draws near, a believer's dream will hardly be false. And the truest vision will be of one who is himself the most truthful in speech, for the vision of a Muslim is the forty-fifth part of Prophecy, and dreams are of three types:
There are 3 kinds of dreams in Islam:
-The dream stemming from personal desire (Nafsani i.e., from desire)
-The dream coming from the devil (Shaytani i.e., from devil)
(Sahih Al Bukhaari, 6499, Sahih Al Muslim 2263and Sahih Sunan Ibn Maajah, 3155)
Imaam al-Baghawi said: Know that the interpretation of dreams falls into various categories. Dreams may be interpreted in the light of the Qur’an or in the light of the Sunnah, or by means of the proverbs that are current among people, or by names and metaphors, or in terms of opposites. Sharh al-Sunnah, 12/220
He gave examples of this, such as:
Interpretation in the light of the Qur’an: such as a rope meaning a covenant, because Allah سبحانه و تعالى says (interpretation of the meaning): “And hold fast, all of you together, to the Rope of Allah” Qur’an.Surah A’le ‘Imraan 3:103
Interpretation by means of proverbs: such a digging a hole meaning a plot, because people say “Whoever digs a hole will fall in it.”
Interpretation by means of names: such as seeing a man called Raashid meaning wisdom.
Interpretation by means of opposites: such as fear meaning safety, because Allah سبحانه و تعالى says (interpretation of the meaning): “And He will surely give them in exchange a safe security after their fear” Qur’an.Surah Noor 24:55
What a person should do if he sees a dream that he/she dislikes
1- He should know that this dream is from the Shaytaan who wants to cause him grief, so he should annoy the Shaytaan by not paying any attention to him.
4- He should spit drily to his left three times, i.e., blowing with a little bit of saliva.
5- He should not tell anyone about it.
6- He should turn over from the side on which he was sleeping, so if he was lying on his left side he should turn over to his right side, and vice versa.
7- He should get up and pray.
Wet dreams are something natural, and they cannot be gotten rid of. Allah سبحانه و تعالى has created desire in man and He has commanded His slaves to use this energy in the proper manner, which is marriage for those who can afford it, in order to attain worldly interests such as building families, strengthening society and populating the earth according to the laws of Allah سبحانه و تعالى. A person who is sleeping does not know what he is doing, so he is one of those from whom the Pen is lifted (i.e., his deeds are not recorded). Wet dreams happen when a person is asleep, so they are among the things that are forgiven.
Allah سبحانه و تعالى has in fact made wet dreams [al-hulum] one of the signs of puberty. Similar to men, women too gets wet dreams as mentioned in the hadith, Umm Sulaym came to the Messenger of Allah صلى الله عليه و سلم and said, ‘O Messenger of Allah, Allah سبحانه و تعالى is not too shy to tell us the truth. Does a woman have to do ghusl if she has a wet dream?’ The Prophet Muhammad صلى الله عليه و سلم said: ‘Yes, if she sees water (a discharge).’ Umm Salamah(R) covered her face and said, ‘O Messenger of Allah, can a woman have an erotic dream?’ He said, ‘Yes, may your hands be rubbed with dust. How else would her child resemble her?’” Sahih Al Bukhaari 130; Sahih Muslim, 313
Based on: "Proclaim the Hajj to mankind" Qur’an.Surah Hajj 22: 27
BLOWING: Blowing away something or someone disliked in a dream indicates that the problem will soon be eliminated. Sahih of Imam Muslim, Sharh an Nawawee vol 8 p 39
Based on: Abu Huraira رضي الله عنه quoted Prophet Muhammad صلى الله عليه و سلم saying "While sleeping, I saw two gold bangles on my hands. This disturbed me, but I was inspired to blow on them, so I blew on them and they flew away. I interpreted the two bangles as the two great liars who would appear after me, and one of them is al Ansee from Sanaa, and the other, Musaylimah, from Yamaamah" Sahih of Imam Muslim, vol 4 pp 1228-9 no 5650
DATES: If one sees fresh dates in a dream, it indicates that one's practise of the religion will become better.
Based on: Anas ibn Malik رضي الله عنه quoted Prophet Muhammad صلى الله عليه و سلم saying "Last night I dreamt that we were in the house of Uqbah ibn Raafi and were brought some Ibn Taab fresh dates. I interpreted it as meaning that eminence in this world will be granted to us, a blessed hereafter, and that our religion has become good" Sahih of Imam Muslim, vol 4 p 1228 no 5647; Sunan of Abu Dawood, vol 3 p 1397 no 5007
GOLD: Being given gold or finding gold may indicate finding a suitable wife or a successful marriage. The symbolism is derived when the Prophet Muhammad صلى الله عليه و سلم restricted ornaments of gold to women.
Based on: Abdullah ibn Zurrayr related that he heard Ali ibn Abi Talib say that the Prophet Muhammad صلى الله عليه و سلم took some silk in his right hand and some gold in his left hand. Then he said, "These two are forbidden to the males of my nation" Sunan of Abu Dawood, vol 3 p 1133 no 4046; an Nasaee and Ahmad
LAUGHING: Dreaming of oneself laughing in a dream may refer to the arrival of good news, good times. Sharh as Sunnah, vol 12 p 221
Based on: "Some faces on that day will be bright, laughing and rejoicing at the good news" Qur’an.Surah Abasa 8: 38-9
MARRIAGE: Dreaming of oneself getting married may indicate an impeding marriage. If there are no marriage plans at the time of the dream, one may propose to the women shown in the dream.
Based on: Aisha (R) said: Allah's Apostle said to me, "You were shown to me twice (in my dream) before I married you. I saw an angel carrying you in a silken piece of cloth, and I said to him, 'Uncover (her),' and behold, it was you. I said (to myself), 'If this is from Allah سبحانه و تعالى, then it must happen.'Later I dreamt of the angel carrying someone in a silken piece of cloth, and I said (to him), 'Uncover (her),' and behold, it was you. I said (to myself), 'If this is from Allah سبحانه و تعالى, then it must happen.' " Sahih Al Bukhari vol 9: 140
MILK: Receiving milk in a dream means that religious knowledge has been granted.
Based on: Abdullah ibn Umar رضي الله عنه said: Allah's Apostle said, "While I was sleeping, I was given a bowl full of milk (in the dream) and I drank from it (to my fill) till I noticed its wetness coming out of my limbs. Then I gave the rest of it to 'Umar bin Al-Khattab رضي الله عنه." The persons sitting around him, asked, "What have you interpreted (about the dream) O Allah's Apostle?" He said, "It is (religious) knowledge." Sahih of Bukhari vol 9 :135