Best way to feel confident is through experience. Don't worry what people think, and don't worry about things not working all the time. If you are true to yourself in the way that you talk to people, the right people will be attracted to you in life as friends or partners. Just go for it! You're still young for worrying so much about consequences, right now in your life there really aren't nearly as many, so might as well get it over with while you can!!
I like someone but like some people I'm shy, so i don't have the guts to go up to them and say hi because i get nervous. I wanna talk to them because i wanna move on from a past relationship.