Androgen
Androgen is a hormone that tells the body to grow muscle, bone, and hair during puberty.
Think of it this way
Androgen is like a switch on a kitchen stove burner. When you flip the switch, the burner heats up and does its job. The switch itself does not cook anything. It just signals the burner to activate. In the body, androgen is the switch and target cells are the burners.
Explaining androgen by grade level
Your body makes tiny signals that tell it how to grow. One signal helps build strong bones and muscles. In one study, rats that got extra of this signal gained more weight. The signal acts like a note that says grow more.