Marriage was instituted by God Himself in the Garden of Eden and restored to such -- raised to the dignity of a Sacrament -- by Jesus Christ in the New Law. The Sacrament's external sign is the freely entered into contract made between a validly baptized man and validly baptized woman who intend to form a marriage and who have no impediments to marriage (or who have any required dispensations if an impediment exists). Like Holy Orders, once the Sacrament is received, it cannot be set aside; a valid sacramental marriage lasts until the death of one of the spouses.
The matter of the Sacrament is the mutual, freely-given consent of the man and woman before a priest and two witnesses. The man and woman are the actual ministers of the Sacrament, and the fruits of the Sacrament are the graces needed to raise a family and live up to the marital vows.
This must be made clear: the primary purpose of marriage is the procreation and education of children, most especially educating them to know, love, and serve God; its secondary purposes are "mutual society and help, and a lawful remedy for concupiscence" (Catholic Encyclopedia). Marriage grants to each partner the right to the spouse's body; the obligation this creates on the part of each is called the "marital debt." I Corinthians 7:1-4:
Now concerning the things whereof you wrote to me: It is good for a man not to touch a woman. But for fear of fornication, let every man have his own wife: and let every woman have her own husband. Let the husband render the debt to his wife: and the wife also in like manner to the husband. The wife hath not power of her own body: but the husband. And in like manner the husband also hath not power of his own body: but the wife.
If both spouses mutually agree to not exercise their marital rights, theirs is said to be a "Josephite marriage" akin to the marriage of Mary and Joseph, but if the marital rights are exercised, the marital act must be open to life. Artificial contraception is strictly forbidden, and the use "natural family planning" (often abbreviated as "N.F.P.") may only be used in grave circumstances and never with a "contraceptive mentality." For a fuller view of Christian marriage, see Pope Pius XI's Casti Connubii and Pope Leo XIII's Arcanum.
If the couple are both baptized and in a state of
grace (couples should make a general confession and receive Communion as soon
before marriage as possible), and none of the impediments listed above exist (or
a dispensation has been gotten), the first thing to do is to announce your
betrothal to your priest, who will then publish the "banns of marriage." The
banns are a public announcement of the upcoming marriage so that any impediments
can be discovered. This "publication" is usually made on three consecutive Holy
Days (including Sundays), during the Mass itself (before or after the sermon)
and/or in the parish bulletin (for good reason, sometimes the banns may be
dispensed with). Then you will obey the civil laws of the State in which you
live by getting the proper blood tests, licenses, etc.
As far as wonderfully girly wedding plans go, I will note here that the bride's dress (and bridesmaids' dresses) must conform to the same rules of modesty and decorum that apply any time a woman enters a church, i.e., her head must be covered, the dress must cover the knees when standing or sitting, the neckline should be modest, etc. No spaghetti strap, totally sleeveless, backless, side-split, mini-length, plunging neckline, sassy little Vera Wang numbers allowed. Of all the days of her life, the last day a woman should want to present herself to the world as sex object is the day she gives herself totally to her husband in marriage. (Note that for a second marriage, or for the marriage of a couple that has lived together in sin and repented, the wedding festivities should be a tad subdued; allusions to virginity, such as the bride wearing white, should be avoided.)
Music is handled differently at Catholic weddings, too. No "Sunrise, Sunset," no Celine Dion tunes -- quite possibly, not even Wagner's or Mendelssohn's Wedding Marches. Save "Unchained Melody" for your first dance at the reception and "At Last" for the cake-cutting; music during the wedding itself must be sacred.
As to the Rite of Marriage itself, it can be offered with or without a Mass and Nuptial Blessing (traditionally, the Nuptial Mass and Blessing are only offered when the bride and groom are both Catholic, not in the case of mixed marriages). If the couple wants a Mass and Nuptial Blessing, the form of the Mass will depend on the day of the wedding. The default Mass offered is the Nuptial Mass (color white) -- but this Mass may not be said on: Sundays; on Holy Days of Obligation; on Feasts of the 1st or 2nd Class; on Ash Wednesday; during Holy Week; on All Souls Day; on the Vigils of Christmas or Epiphany or Pentecost; or within the within the octaves of the Epiphany, Easter, Pentecost, and Corpus Christi. If a wedding takes place on any of the above days and a Mass is desired, that day's Mass is said (and the color will be of the Mass of that day) instead of the Nuptial Mass, but the Collect, Secret, and Postcommunion prayers from the Nuptial Mass are added to it along with a prayer for the couple after the Pater Noster, and a blessing for the couple.
Impediments to a sacramental marriage are of two
types: diriment impediments, which render an alleged marriage null and void or
make a potential marriage impossible, and prohibitory impediments, which don't
affect validity but liceity (i.e., its strict accordance with Canon Law) and
require a dispensation first.
Diriment impediments include: the inability to freely consent; blood relationship to the fourth degree collaterally, or in any degree in the direct line; relationship by adoption if the relationship is to the second degree collaterally, or in any degree in the direct line; spiritual relationship, such as that between godparents and godchildren; a solemn vow of chastity; impotence (not sterility) that is known and not revealed; having been a party in a marriage contract that was not ended by death or found to be invalid with a declaration of nullity (an "annulment") or dissolved by the Petrine or Pauline Privileges (see below); having received Holy Orders; not having reached the age of 14 (women) or 16 (men); if either of the couple is not baptized. If one of these impediments exist, a marriage cannot take place (only in very, very rare cases are dispensations given to a couple who have affinity in the first degree of the direct line).
Prohibitory impediments include: betrothal to another (i.e., pledge of marriage to another); a simple vow of chastity; if one party is baptized but belongs to a schismatic or heretical sect; lack of parental consent in the case of minors. If one of these impediments exist, a marriage would still be valid, but a dispensation must be gotten in order for the marriage to be licit.
If any of these impediments exist, the couple is bound to declare them.