When one stimulates the genetilia. For guys, it involves taking their hands and gently rubbing up and down on their cock and they seem to get harder and harder and start rubbing faster until he cums all over the place, he also will get VERY horny and have an orgasim. For girls, it involves sticking one, two, three, four. or how ever many fingers or a foreign object in their vagina hole; often called "sticky fingers" becasue your fingers do tend to get sticky, but its pleasurable. You tend to do it while having cyber sex or looking at dicks.... it gets you very horny and you reach a HUGE orgasim.
I can't come down for dinner right now, I'm too busy masturbating and it feels SO good!