Islam, unlike other religions is a strong advocate of marriage.  There  is no place for celibacy like, for example the Roman Catholic priests and   nuns. The prophet (pbuh) has said  "there is no celibacy in Islam. 
 Marriage is a religious duty and is consequently a moral safeguard as  well as a social necessity.  Islam does not equal celibacy with high "taqwa" /  "Iman". The prophet has also said, "Marriage is my tradition who so ever keeps  away there from is  not from amongst me".
Marriage acts as an outlet for sexual needs and regulate it so one does  not become a slave to his/ her desires.It is a social necessity because through marriage, families are  established and the family is the fundamental unit of our society.  Furthermore,  marriage is the only legitimate or halal way to indulge in intimacy between a man  and a woman.
 Islam takes a middle of the road position to sexual relations , it  neither condemns it like certain religions, nor does it allow it freely.  Islam controls them and regulates their desires,  whatever they may be so that they remain dignified.
To make the marriage legit.
    1) consent of both parties. 
   2) " Mahr" a gift from the groom to his bride. 
   3) Witnesses- 2 male or female. 
   4) The marriage should be publicized, it should never be kept  secret as it       leads to suspicion and  troubles within the community.