Be very nice to them. Nuns can still hit. :D!
I mean...Just make the best of it. They won't hurt you. It's like a normal high school, but Catholic. And yes, you are going to hear much about religion. But that's because it's a religious school, intended for folks that believe in or are willing to learn it. Still, it's like any other school - You get the experience you choose to draw from it. Good luck. c: