I like a girl but have no idea what to do

So there's this girl I went to school with and she's always seemed really cool, we never really talked we just had mutual friends, anyway I added her on Snapchat and she added me back like a week later. I don't really use snapchat nor understand it much but I don't have her phone number or anything. She sent me a snap but the photo was just like a quarter of her face and a wall. But it seems that's just what people do on the app, and like I know that doesn't been she necessarily interested in me at all obviously, but I sent her a simple snap back and we've been going back and forth once or twice a day, only for a few days now but I sorta wanna start a conversation with her, even if its light, I just don't know how exactly (and I lack confidence lol). I just want to play my cards right, even if she just wants to be friends I would like to get to know her more.

If anyone has any advice I would love to hear it.