The first part of learning to play a wind instrument (clarinet, flute, trumpet, etc.) is learning how to breathe.
Muscles can only do two things: contract and relax. Lungs are controlled by two muscle groups: the diaphragm and the chest.
The muscles in the front of the chest are the most obvious, and the least important: they only squeeze the air out, which doesn't really take active effort most of the time.
The diaphragm is what pulls air in to the lungs. It does this by pulling the lungs straight down toward the stomach.
Practicing this intentionally, by pulling your diagram down and holding it, is great exercise. Deeper slower breaths are more effective at cycling oxygen and CO2 through the blood stream, help you speak louder and longer, and can even significantly reduce your stress level.
Breathing is something we do automatically well enough, but breathing intentionally is incredibly useful.
