Hello deweyph. First of all, congratulations on your engagement.
According to the Code of Canon Law:
Canon 1118 §1. A marriage between Catholics or between a Catholic party and a non-Catholic baptized party is to be celebrated in a parish church. It can be celebrated in another church or oratory with the permission of the local ordinary or pastor.
§2. The local ordinary can permit a marriage to be celebrated in another suitable place.
§3. A marriage between a Catholic party and a non-baptized party can be celebrated in a church or in another suitable place.
The term “local ordinary” refers to the bishop of the local diocese. What constitutes “another suitable place” is determined by Catholic norms and the policies of one’s diocese. Therefore, if you desire for the wedding to take place in a location other than a Catholic church building, you will need permission from your bishop (i.e., the dispensation you mentioned) and such permission may or may not be granted depending on exactly what you have in mind. I’ll speak more about the process of getting dispensations from a bishop in a moment.
Your girlfriend does not need to convert to Catholicism in order to be married to you, or for the marriage to take place within a Catholic church building. The Catholic Rite of Marriage has a version which is done within the context of a Mass (i.e., the Nuptial Mass) and a version which is not (i.e., a Scripture service without the celebration of the Eucharist). If a Catholic and a non-Catholic are married within a Nuptial Mass, of the couple only the Catholic person would receive Communion (please see the Catholic Answers tract
Who Can Receive Communion?, scrolling down to the heading, “Other Christians and Communion”).
If your girlfriend desires to become Catholic and, consequently, receive Communion at Mass then that would normally be done through the
R.C.I.A. process in a local parish. Naturally, this should stem from a sincere desire to fully embrace the Catholic Faith as part of her spiritual journey and not simply for the sake of receiving Communion at the wedding.
In any event, the first step is to make an appointment in your parish with a priest or deacon (or a properly trained and designated layperson) to start the marriage preparations. Even if you decide to have the wedding inside a Catholic church building, Canon Law requires that you get a dispensation from your bishop in order to marry a non-Catholic (so one way or another, the bishop would need to be involved). However, you do not need to actually meet with the bishop, as such matters are handled through the staff of your parish (i.e., they will act as your liaison with the bishop’s office).
