Acne is a normal part of puberty. Your body makes hormones that make your face oily, which can cause pimples. Oil glands in the face are usually more active in guys than girls, so your acne can be worse.
You can't stop acne from happening, but you can cut down on breakouts by washing your face twice a day. Don't scrub too hard, though. Tougher cases may need over-the-counter or prescription medication.