It’s probably going to be extremely foreign to you. If what you attend is an average (Low) mass, you won’t hear much of the Latin to begin with, as it’s said almost inaudibly by the priest. If you do, however, go to a High Mass (less likely) you will hear a lot of Latin. But in all likelihood, you’ll probably be at a Low Mass.
Anyways, there’s going to be a lot of kneeling. So get used to that. It’ll be done on these things called “kneelers,” which flip out from the pew in front of you. There will be a lot of gestures made and postures assumed which you will know nothing about. The main thing, if you want to fit in and respect your surroundings, is this: sit when everyone sits, kneel when they kneel, and stand when they stand. If you want to be on “observatory mode” and just watch without any participation, I suppose you could do that by sitting in one of the furthest-back pews, where you would be unnoticed if you weren’t sitting, standing, and kneeling with everyone else, which is fine, but like I said, do this in one of the furthest-back pews so it doesn’t distract anyone else. You’re not expected or even encourage to give money when that time comes around, because you’re not a parishioner, but feel free if you want to.
Try to absorb as much of the mass as possible. The smells, bells, artwork, and the absolute silence. If the church is anything like most that offer the Tridentine Mass, it will probably be extremely quiet both before and after the mass. Do dress appropriately. Appropriately meaning modestly, cleanly, and presentably. You don’t have to dress for a date, but be sensible, that’s all. If you’re a woman, you may want to cover your head with a mantilla or a hat of some sort, but this is not required.
This is probably the most important thing. I’m sure you’re aware that the Eucharist (“Communion”)–the consecrated bread and wine which Catholics hold to be the true, real, Body and Blood of Christ–is made present at every mass. That’s what mass is, the celebration of this Body and Blood being made present. You will notice that many, if not most, of the congregation will approach the priest to receive the Body of Christ, which they will consume. Do NOT do this! Only Baptized Catholics may receive the Body (and Blood) of Christ. This is not because Catholicism is some “exclusive club,” but because the Catholic Church teaches that people must be properly “catechized” (taught) about the meaning of the Eucharist, and many other things about It. You have not been catechized, therefore you may not receive the Eucharist. I can’t stress that enough. Don’t go up to receive Communion. You may find that others are in your pew, and you may let them out so that they may go receive Communion, but when they have left, just sit back down. You might feel weird to be one of the only ones–or the only one–to be sitting instead of receiving Communion, but this is proper and doctrinally correct.
