Nikah is an Arabic term used for marriage. It means "contract" ("aqd in Arabic). The most important thing is that it keeps you chaste from adultery, from fornication and the loss of lineage, and from the corruption of moral uprightness. There is the protection of one’s health. 
The Quranspecifically refers to marriage as "mithaqun ghalithun," which means "a strong covenant". "...and they have taken a strong pledge (mithaqun ghalithun) from you?" Quran Surah Nisa 4:21
These are the main characteristics that should be sought when choosing a spouse:
Deen (way of Life as prescribed by Allah): It is the first thing to look for according to The Prophet Muhammad’s (May Allah honor Him and grant Him peace) instructions. This does not mean choosing any Muslim but the one who applies Islam throughout his daily life, not just a nominal Muslim.
"A woman may be married for four reasons: for her property, for her rank, for her beauty, and for her religion (and character), so marry the one who is best in the religion and character and prosper." Sahih Al Bukhari Vol 7:27 or 5090(NE) and Sahih Al Muslim 3457 and Ibn Majah, Vol 1:595. Prophet Muhammad (May Allah honor Him and grant Him peace) assured the bounty of Allah to those who wish to get married and live a pure and clean life.
Conduct: A woman or a man who has good manners is considered as a grace from Allah (Glory be to Him). The Prophet Muhammad (May Allah honor Him and grant Him peace) said, 'There is nothing more beneficial to a believer next to the fear of Allah (Glory be to Him) than a pious wife. When he commands her, she obeys him; and when he looks at her, she pleases him; and when he swears by Allah (Glory be to Him) that she should do a thing, she would; and when he is away, she guards herself and his property.' Musnad Ahmad Vol 2:251; classed as hasan by al-Albaani in al-Silsilah al-Saheehah 1838.
This also applies to the husband with regard to good conduct and fear of Allah (Glory be to Him), for raising children requires the efforts of both parents not just one of them. Since man is the head of the family, it is his responsibility to choose a pious woman to be the mother of his children. Allah (Glory be to Him) states, 'O you who believe, protect yourselves and your families from a fire whose fuel is man and stones.' Qur’an.Surah Tahrim 66:6
And Allah (Glory be to Him) says, 'And enjoin as-Salaat (the prayer) on your family, and be patient in offering them [i.e. the Salaat - prayers].' Qur’an.Surah Taha 20:132
When The Messenger of Allah (May Allah honor Him and grant Him peace) was asked about the greatest sins, he replied, 'You should associate an equal to Allah (Glory be to Him) while He created you, that you kill your child out of fear that he would eat from your food, and that you commit adultery with your neighbour's wife.' Sahih Al Muslim 157 and 156.
The prohibition of killing one's children is a necessary consequence of having mercy for them and protecting their body, minds and soul from harm. 
Islam gives utmost importance to marriages. Marriage is the most basic remedy for sexual appetite.
Under the Shari'ah (Islamic Law), marriages between men and women standing in a certain relationship to one another are prohibited. These prohibited degrees are either of a permanent nature or a temporary. The permanently prohibited degrees of marriage are laid down in the Qur'an: And marry not those women whom your fathers married, except what has already happened (of that nature) in the past. Lo! it was ever lewdness and abomination, and an evil way. Forbidden unto you are your mothers and your daughters, and your sisters and your father's sisters and your mother's sisters, and your brother's daughters and your sister's daughters, and your foster-mothers and your foster-sisters, and your mothers-in-law and your step-daughters who are under your mother-in-law and your step-daughters who are under your protection (born) of your women unto whom you have gone into -- but if you have not gone into them, then it is no sin for you (to marry their daughters) -- and the wives of your sons from your own loins, and that you should have two sisters together, except what has already happened (of that nature) in the past. Allah is ever-Forgiving, Merciful. Qur’an.Surah Nisa 4:22 - 24)
From the above Ayah, it is clear that a Muslim must never marry the following:
A great wisdom lies behind these prohibitions on the grounds of consanguinity, affinity, and fosterage. No social cohesion can exist if people do not keep these prohibitions in their minds while contracting marriages.
Temporary prohibitions are those which arise only on account of certain special circumstances in which the parties are placed. If the circumstances change, the prohibition also disappears. They are as follows:
The assembly of Nikah is addressed with a Nikah Sermon (khutba-tun-nikah) by the Muslim officiating the marriage. In marriage societies, customarily, a state appointed Muslim judge (Qadhi or Qazi) officiates the nikah ceremony and keeps the record of the marriage contract. However any trust worthy practicing Muslim can conduct the nikah ceremony, as Islam does not advocate priesthood. The documents of marriage contract/certificate are filed with the mosque (masjid) and local government for record.
Prophet Muhammad (May Allah honour Him and grant Him peace) made it his sunnah to have Nikah sermon delivered in the assembly to solemnize the marriage. The sermon invites the bride and the groom, as well as the participating guests in the assembly to a life of piety, mutual love, kindness, and social responsibility.
The Khutbah-tun-Nikah begins with the praise of Allah (Glory be to Him). His help and guidance is sought. The three Quranic aayath (Qur’an.Surah An-Nisa' 4:1, A’le ‘Imran 3:102, Al-‘Ahzab 33:70-71) and one Prophetic saying (hadith) form the main text of the marriage.
Prophet Muhammad (May Allah honour Him and grant Him peace) considered simple weddings the best weddings, 'The best wedding is that upon which the least trouble and expense is bestowed". (Mishkat)
There is nothing wrong with any Muslim person reciting Khutbah al-Nikaah before the ‘aqd (contract) is made, but it is a condition that the guardian of the bride be present. He should say to the groom, “I marry my daughter So-and-so to you,” and the groom should say, “I accept.” This should be witnessed by two Muslims, and the bride should give her consent, in order for the contract to be valid.
Khutbah al-Nikaah is the same as Khutbah al-Haajah, which the Prophet (peace and blessings of Allaah be upon him) taught his Companions, and it should be said at the beginning of the ‘aqd. This is sunnah, not waajib(obligatory).
Al-hamdu Lillaahi nasta’eenahu wa nastaghfiruhu, wa na’oodhu billaahi min shuroori anfusinaa wa sayi’aati a’maalinaa. Man yahdih Illaahu falaa mudilla lahu wa man yudlil falaa haadiya lahu. Wa ashhadu an laa ilaaha ill-Allaah wa ashhadu anna Muhammadan ‘abduhu wa rasooluhu . Meaning is Praise be to Allaah, we seek His help and His forgiveness. We seek refuge with Allaah from the evil of our own souls and from our bad deeds. Whomsoever Allaah guides will never be led astray, and whomsoever Allaah leaves astray, no one can guide. I bear witness that there is no god but Allaah, and I bear witness that Muhammad is His slave and Messenger
Then the following three aayaat are recited: ‘Yaa ayyuha’lladheena aamanu-ttaqu’Llaaha haqqa tuqaatihi wa laa tamootunna illaa wa antum muslimoon (O you who believe! Fear Allaah as He should be feared, and die not except in a state of Islam (as Muslims) with complete submission to Allaah.)’ [Qur’an Surah A’al ‘Imran 3:102], ‘Yaa ayyuha’n-naas uttaqu rabbakum alladhi khalaqakum min nafsin waahidatin wa khalaqa minhaa zawjahaa wa baththa minhumaa rijaalan katheeran wa nisaa’an wa’ttaqu-Llaah alladhi tasaa’aloona bihi wa’l-arhaama inna Allaaha kaana ‘alaykum raqeeban (O mankind! Be dutiful to your Lord, Who created you from a single person, and from him He created his wife, and from them both He created many men and women, and fear Allaah through Whom you demand your mutual (rights), and (do not cut the relations of) the wombs (kinship) Surely, Allaah is Ever an All-Watcher over you).’ [Qur’an surah al-Nisaa’ 4:1], ‘Yaa ayyahu’lladheena aamanu-ttaqu’Llaaha wa qooloo qawlan sadeedan (O you who believe! Keep your duty to Allaah and fear Him, and speak (always) the truth).’ [Qur’an surah al-Ahzaab 33:70].” 
 http://islamqa.info/en/2068 and 2066