Oral - What makes it so good?

Jen® • I`m 19 and think I know more than I actually do. Young & Dumb.
 So the guy I'm with now is the first to ever go down on me. I never knew what to expect from it, like I always thought it'd be cold, but it wasn't. It feels good, but not THAT good, like not enough to make me finish. What makes oral so good? Maybe he's not doing it right, I don't know. He's made other girls finish before, but I just can't get into it. 
So for you ladies that enjoy it, how long was it until you began to enjoy oral??