What should I do about this girl?

K so, there's this one girl who I really like and I want to go out with her. But the problem is that I don't really know how to talk to girls for some reason. We always say hi to each other when we see each other in the halls at school, but that's all we do! I want to be able to know how to talk to her better and start conversations with her so I can go out with her. I want to be bale to talk to her but I really don't know what to say. Can someone please help me on this??? (btw im in 9th grade and we're both 15)