I am an un-popular girl, and I like a popular boy. And he likes me too!...?

He is in the same year as me. He really seems to like me too. Everytime I look at him, he's looking at me. Sometimes, when I am alone, he will walk past me for no reason, and say hi. He hangs out with other people, we don't even know each other properly yet. I want to talk to this guy, but I'm not the most confidant girl. I am not a good conversation opener. I can't even say hi to him! If anyone has had a similar thing happen to them, and if they've worked through it, please give me some tips. Anyone can give tips.