What should I do to start a relationship?

Okay so I have a crush on my sister's old friend from elementary school. They don't even talk anymore but still I haven't told her. I haven't told anyone except for my two closest friends. So me and my crush don't even really know each other like that. We saw each other at the mall once and he made me laugh by being really sarcastic (he's really funny) and that was kind of it. I mean all we did is say hi and when my friend and I were about to leave he made me laugh. But just recently I befriended him on facebook. What I want to know is how do I start my own relationship with him? I can't use my sister because like I said my crush and her don't talk anymore and I haven't even told her I like him. He doesn't really know me all that well. There is a 3 or 4 year age difference. He likes to skateboard. That's like his passion. Can I start talking to him without it being weird? Help please. Thanks in advance :)