How do I find out if I'm bi, or not?

Hi! I am a 15 year old female and I think I may be bisexual, I have talked to a couple friends (who are straight) that I trust, They either said "It's just a phase don't worry" Or "There is only one way to know and that is to have sex/kiss another female." But I don't know any lesbian girls to do that with! I'm pretty sure it's NOT a phase but I need to know how to find out if I'm bi or not....

I'm into my friend and want to fool around with her, but will she do it?

Samuel F.
I'm 15, and I have a close female friend of the same age with D-cup bra size and very good looks all-around. She hasn't shown much visible interest in sexuality, but we haven't talked very much about it at all. I've been wanting to see if she'd want to fool around. Is that really way too much for friendship or could I somehow get her to do it willingly?...