The cells of the brain require oxygen and energy in order to function properly. If there is not enough oxygen or energy available, your thinking slows down and you become tired. This is why it is useful to go outside and eat properly during long school days. 

Energy must be supplied to the brain regularly during the day. This does not mean that your brain needs energy drinks, however. Eating and drinking sugar-rich foods and drinks provides only a temporary energy boost. 

Your brain also needs rest. The best form of rest is sleep.

Different substances, such as drugs and alcohol, have a detrimental effect on the brain. This is why children and responsible people should never touch such substances.