Let your partner do all the movement. If you go limp, try again or switch to something else. Make sure it's all right with you and your friend if you go limp, since this (limp=failed=bad) can be the biggest part of feeling like you're no good. Take time discovering that you can be erect and be inside him. If it doesn't happen sooner or later, you may want to just let it rest until a better time.

After you feel comfortable being inside them, try moving. As you begin to do this, open up to your desire. Try the side-ways position, both facing the same way, since it won't be as demanding as some others. Once you feel fluid and relaxed mentally, your body will flow also. Flex it; try out your pelvis. Just move it around any old way and see what happens. You'll probably discover most if not all the possible movements. Thrusting is with the small of the back (just above your ass), making your pelvis tip up and down. You'll be rusty at first; practice makes better (dancing is also a good place to practice).

You'll find you can move in ways that express your feelings: slow, fast, hard, soft, simple, complex, as you like. Also it'll take time to coordinate your movements with theirs; this cooperation is learned, as you pick up each other's styles and talk about what's good for you. If both of you are into moving at the same time, perhaps the easiest is for you to thrust while your partner rotates their pelvis.