God is a God of Love. As love is very important including couples who truly love each other, He united man and woman as one under the Sacrament of Matrimony.
The Sacrament of Matrimony binds a baptized man and a baptized woman in a lawful marriage for life. Its primary purpose is to begetting and rearing of children in the fear and love of God.
The groom and bride are the ministers of this sacrament. While the Priest is the witness authorized by the Catholic Church to present and bless the union of this couple.
God institutes this Sacrament when He created Adam and Eve in the Garden of Eden (Genesis 2:24). Before it was only a Sacred Contract, but when our Lord Jesus Christ came, He raised the Matrimony to the dignity of a sacrament.
A Man and a Woman who are in legal age of marriage, unmarried and both Catholics.
Those who are not Catholics. Also, same sex marriage is not allowed in the Catholic Church. God only created Man to unite with a Woman.
No. Catholic Church Wedding is a marriage under the law of God which cannot be broken. While Civil Wedding is under the law of Man and can be broken by having legal procedures.
Source:
http://www.sspxridgefield.com/sacraments,