Most Helpful Girl
Rejection is normal. Not everyone in supposed to love everyone and anyone. You have to find "your person" based on common interests, similar background and stuff. What's about sex, well, when I first saw my future husband, I thought I'd never ever sleep with him. But got on very well and we developed such chemistry that our neighbours can hear us and our bed can barely hold itself together. So, don't get upset if some girl won't do one night stand with you.
Most Helpful Guy
Ask yourself honestly, what do you lose by trying? If you're looking for sex then go out to a bar/club with friends, get drunk, ask a girl if she wants to dance with you.
If you're looking for more, ask a girl you have an interest in if she wants to go for lunch - something small. If she says no, consider how many other women there are to ask.
Honestly, it's a numbers game when you first start out. Try it on with girls you normally wouldn't think to and build your confidence from there.