what exactly is the sacrament of marriage?

The Catechism tells us that, "The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament." (CCC, 1601). The Sacrament of Matrimony is a very unique sacrament because it is one that the Bride and Groom give to each other. The priest is simply a witness to the sacrament. It is in this sacrament that a man and a woman give and receive one another and join as one flesh, being sealed by God Himself. The grace in this sacrament "perfect[s] the couple's love and strengthen[s] their indissoluble unity. By this grace they help one another to attain holiness in their married life and in welcoming and educating their children." (CCC, 1641). 

how do i go about receiving the sacrament of marriage?

Adults who wish to receive the Sacrament of Marriage must contact the parish office a minimum of six months in advance for Marriage Preparation Classes. No wedding dates are made by phone. Minimum age is 18 and marriage preparation is required.