There is this girl in my school, in my year I have no lessons what so ever with her and I like her but I don't know if she likes me and also I haven't asked her out yet because I'm scared she will say no! Please help

Are you friends?

Are there other times such as before or after school, clubs, library, in the halls, etc. when you could approach her? Do you have any friends in common? Do you have classes with any of the people she hangs out with who you could go up and talk to when she is with them? It would give you a chance to get to know her a bit better and find out if she is currently dating anyone.

If she is available, why not ask her to a school function like a game or dance? The worst she can do is say 'no'.

Not sure of your age, but back in the day we just introduced ourselves, and see if we could call them after school. Before school, during lunch between classes, whenever you see them, say something. Start with HI, I am..

Do you know each other?If you don't know her I think you should just leave it.If she does know you then just go for it!