New school, new people.

Hello friends, I am moving to a new high school! I'm going to a be a 15 year old sophomore (just moved) and I need your advice! I haven't accepted my homosexuality until this summer so I have no gay experience with school. So I am so confused! How do I know if someone is gay? How should I tell everyone? What if I'm bullied for it? How do I ask a guy out? Thanks for your help!