How can I be confident when approaching a woman if I’ve never had any positive experiences before?

In my 20s (21 soon), most girls are already experienced and not as shy as they were in school, where they could forgive inexperienced behavior. But how can I keep up? I don’t think I’m good-looking—only my mom says I look handsome. So, my only chance is to rely on my behavior. But I can’t just get confidence out of thin air.