At your age, you are very active. Most of the time you are working or playing. Surely you feel tired also.
When your body is tired, stop working or playing. Rest until the tired feeling is gone. the tired feeling is a sign that your body needs rest. What happens when the body is at rest?
Many parts of your body like your heart, lungs, stomach and muscles are working all the time. When you rest,these parts of your body slow down their work. This gives them a chance to rest too.
