"I'm afraid to be on top because I don't know how to do it. Any advice?"
I'm afraid to be on top because I don't know how to do it. I have tried it but I can't. Do you have any advice?
Let's start with the basics. Wait until he's erect, then simply straddle him. He lies on his back, you put your legs either side of his hips and lifting yourself above him, hold his penis, lower and guide him inside you.
If your knees are on the bed, you then use your thigh muscles to move yourself up and down on his penis. Some girls find it easier to squat, with their legs bent and feet on the bed instead.
Picture a frog and you get the idea! Try it that way to see which I easiest. Also experiment with leaning forward and leaning back.
If you seriously can't get the hang of thrusting in the traditional style, don't try. Either let him take over, grind yourself against his pelvis making little circles or rock back and forth.