Cradle Catholics pick this stuff up from, well, life.
We converts have to read. A lot. LoL.
This book seems to get good reviews, in a general overview of Catholicism (the responses, the sacramentals ((Holy Water, medals, etc)) the ‘etiquette’ of Catholicism)
amazon.com/gp/product/0879735902
Now, in theory, there should be a class for people like you - who know doctrines like The Trinity, know about Scripture, who have been baptized, and who can speak the Christian ‘jargon’. It’s called “The Way” at my parish. Call your local parish to find out if they have something like this.
Usually, however, everyone gets bundled into RCIA, the Rite of Christian Initiation for Adults (because of lack of volunteers to run alternative programs, in my experience). This program starts with Inquiry, where you get a very general overview of Catholicism and decide if you want to continue. After Inquiry comes the deeper study of Catholicism, and then you’re Confirmed and receive Holy Communion at Easter Vigil (the Mass on Holy Saturday, the day before Easter Sunday).
Nobody knows everything though. Here’s a quick look, for you:
When you enter the church there will be small bowl (called a font) just inside the door. Usually attached to the wall. You stick our fingers in it (you can do this even as a nonCatholic) and bless yourself, recalling your baptism, washing away venial sins, and recognizing that you are entering Sacred Space now. To bless yourself ("make the sign of the cross) you touch your forehead, then chest/lower stomach, left shoulder, then right shoulder, saying “In the Name of the Father, and of the Son, and of the Holy Spirit”.
I could give you an entire post on the Sign of the Cross. I love it. It can get into theology, spirituality…lol, there’s a lot that goes on there.
Anyway, you come in, bless yourself with Holy Water, then walk up to a pew. At this point, find a red or white candle hanging next to a golden, or special looking, box or cabinet. Sometimes it has cloth around it too. That ‘box’ is the tabernacle, where the ‘extra’ Communion is kept. (You know our teaching on Communion, yes?) We show reverence to Our Lord by ‘genuflecting’ to the tabernacle (well, really to He who is inside the tabernacle). Genuflecting means to bow your head and ‘take a knee’. Your right knee in this case. Touch your knee to the floor and bow your head = genuflecting. I make the Sign of the Cross when I do this too.
Ok. Now you’re in the pew. Look around for a ‘missal’. This is a book that has the order of the Mass, with our responses in bold. Hopefully one is in the pew. If not, you could try looking near the front door of the Church, but I would just say go ahead and don’t say the responses this time. Just let the Mass wash over you. If you do find one, look in the front. It will say “Order of the Mass”. Ours has the hymns after it.
After Mass is over, wait till the priest passes your pew, then leave, genuflecting again before you go.