that is a great question! You have probably hear people at your school talking about that. When a guy jacks off, that means that he has been masturbating (rubbing the penis for enjoyment and pleasure) to the point where semen is released from the penis. Semen is a whiteish fluid that contains sperm. Semen is also called c u m. When semen is released this is called an ejaculation. When you ejaculate, you get this really good and enjoyable feeling called an orgasm. You might not be able to do this yet. You can definitely masturbate, but if you are still pretty young (10-12) you might not be able to release semen. This is a totally normal thing to do- all guys do it! Just have fun with it!