Hand jobs are a staple in sex, but you need to do it the right way, such as hitting the right spots, using the right techniques.
With the penis laying on the stomach of your partner, it is time to bring him some satisfaction.
You need to take one hand, and cup the exposed testicles. (the scrotum)
Then with the heel of your other hand, gently rub the underside of the penis shaft.
Use an Up and Down motion.