First of all, congratulate your lovely boyfriend on having the courage to ask. How good of him, to be concerned with what you'd most like to happen!
And second, talking about sex frankly while you're NOT having it leads to it being easier to talk about it while it's going on. If you need to, you can practice saying what you want him to do to you while you're alone. Really think about it, figure out what words you're comfortable with. And then, yes, it is a bit of a plunge, but he'll never know what you want unless you tell him.
If you need to know the names for parts of your body or for his, you can check out these links:
Man’s Best Friend – Male Sexual Anatomy
Pink Parts – Female Sexual Anatomy
Also, check out this article:
Sexual Negotiations for the Long Haul
Welcome to Scarleteen, by the way!
"Ooh, I'll settle down with some old story/About a boy who's just like me/Thought there was love in everything and everyone, you're so naive!"-Belle and Sebastian, "Get Me Away From Here I'm Dying"