Breathing is the process of moving air in and out of the lungs. For living organisms with lungs, breathing is also called ventilation, which includes both inhalation and exhalation. In addition to removing carbon dioxide, breathing results in loss of water from the body.
The air we inhale is composed of: 78.62% nitrogen; 20.84% oxygen; 0.96% argon; 0.04% carbon dioxide; 0.5% water vapour
It is not possible for a healthy person to voluntarily stop breathing indefinitely as breathing, together with swallowing, is an unconditioned reflex. If one does not inhale, the level of carbon dioxide builds up in the blood, and one experiences air hunger. If a healthy person was to stop breathing (i.e. hold their breath) for a long enough amount of time, they will lose consciousness, and the body would resume breathing on its own.