The penis is the male sexual and reproductive organ. The penis is external, which means that it is located on the outside of the body. It has two main parts: the shaft and the glans (or the head). The inside of the shaft of the penis is made up of spongy tissue. When that tissue fills with blood, the penis becomes hard. That is called an erection. The head has a lot of nerve endings, which is why touching the penis feels good.

Inside the penis is a tube called the urethra. Urine (or pee) passes through this, as well as semen. Semen comes out of the urethra when a guy ejaculates. Semen contains the sperm, or reproductive cells, that can make a girl pregnant.

Luckily, when a guy has an erection, there is a ring of muscle inside the body that closes off the bladder and makes it impossible for urine to come out.