It all depends on your age. If you're in middle school, they usually make fun of you, hit you or insult you. If you're in highschool, they usually stare at you in class, act like a goof towards you when they're with their friends, and are nice when it's just you. Does this help?
I talk to the girl every chance I get. When it's me her and a group of friends, I'm off the walls. I glance over at her every few minutes in class. I don't actually tell her because I'm trying to figure out the best way. I tell her if she asks me who I like.