Newcomer seeking advice

My home church ostracized my family when I was twelve for my mother's violent alcoholism. I have wanted to come back to church for a while now, and I've had signs to go back and I've felt called, but it's been years since I've been part of a church, and I'm not even sure what or if I believe anymore. I don't know anything about Catholicism because I grew up Protestant, but I want to. I'm going to try to go to Mass tomorrow (alone). What should I know?