As understood within the Catholic Church, marriage is considered a sacrament if both the man and the woman are baptised, are able to marry, freely consent to the marriage, and meet all the other conditions that the church defines in her code of canon law as necessary for a valid sacramental marriage to exist. The Church provides classes several months before marriage to help the participants inform their consent. During or before this time, the would-be spouses are confirmed, if they have not previously received confirmation and it can be done without grave inconvenience (Canon 1065).
The Catholic Church has further requirements for the form of vows, called the "canonical form". The canonical form of marriage must be followed (unless dispensed). The requirement for a canonical form of marriage began due to the reforms of the Council of Trent. With the decree Tametsi of 11 November 1563. Ne Temere promulgated by Pius X, August 2, 1907 added (and continues to enforce) further specifications.
Here are some local and related sites:
Catechism of the Catholic Church on marriage and sexual morality
§ CREATION (§ 355-384)
§ FALL (§ 385-421)
§ ETERNAL LIFE (§ 1020-1060)
§ Sacrament of Matrimony (§ 1601-1666)
§ Ethics of Life (§ 2258-2330)
§ Sexuality and Chastity (§ 2331-2350)
§ Offenses Against Chastity (§ 2351-2356)
§ Homosexuality and Chastity (§ 2357-2359)
§ Marital Sexuality (§ 2360-2379)
§ Offenses Against Marriage (§ 2380-2400)
What makes a Christian marriage different from a secular one?
The Joy of Love by 
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