How do I give my son the sex talk? He's 16

Okay so I guess it's time for the talk about sex or whatever. I don't know how to start it though. He's a football player, usually makes all As and Bs, so even if he knows about sex I doubt that it's on his mind as I raised him to respect himself and respect me. But I think its time he learns about it and then I'll go over abstinence. Im just wondering what do I start with, like the basic things?