How to be friens with a girl through Facebook?

k theres this girl whos in my grade, and we never talked b4. she has never been in any of my classes. i have her on facebook. on facebook she seems so cool and i just want to be friends with her. but idk how in rl cuz it be awkward since were not in any classes together. how can i get to know her through facebook, then make it lead to rl?