Most young people start to feel sexual desire when they enter puberty (read more about the hormones that cause puberty and sexual desire here) and this is perfectly normal. Sexual desire can be very strong and many young people masturbate to release sexual tension and to have an orgasm. Masturbation is a safe way to release sexual tension and does not harm anyone. If you are thinking about having sex with someone else, there is more information to find out if you and your partner are ready for sex here.