I was the first girl my bf dated when he was 18, and I thought it was cute because he did all sorts of sweet stuff that 'experienced' guys don't seem to do. He also didn't pressure me for sex, cuz he was so scared to do it for the first time.
I think girls are pretty patient with an 'inexperienced' guy your age. Now, if you were 25, that might be a different story. Anyways, just take it easy, be yourself, don't expect to be perfect. IF you want to ask someone out, just make it sound nice and casual.......ask what she's doing on a certain day, and suggest getting together to do something. It's pretty harmless, and since you haven't come right out and say "Hey, you wanna go on a date with me?" she won't feel uncomfortable. Good luck. Just go for it, the worst thing that could happen is she says no.......and that's really no big deal.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi