Ugh! Don't listen to guys about how to ask out a girl. This is what you do:
You: Hey (girl's name), what would you say if I were to ask you to go out with me?
You see? Nothing to it. Now don't be a chicken; go and ask. Learning how to do this is a very important step in growing into a man. Yes, some girls will say no, but some will say yes. Dating is a numbers game; if you ask enough girls, one will say yes.
Good luck.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?