Breathing is something an organism can do consciously or sub-consciously. It’s not questioned, you simply must breathe in order to get oxygen to your body, and you must get oxygen to your body in order to survive. The advanced mechanisms of breathing, and the gas exchange of oxygen and carbon dioxide, are more detailed and complex than just letting air in and out..
When a human first inhales, the air enters through the trachea, which is located behind the esophagus. The trachea is lined with various cilia and mucus, the mucus traps dust particles, while the cilia transfer particles to the pharynx, so that they may be swallowed into the esophagus.
The trachea divides into two bronchi, which then separate into bronchioles. Like the trachea, bronchi are also lined with cilia and mucus to pick up any remaining particles. the division continues; the bronchioles are divided into even smaller tubes. Ultimately the division stops in tiny air sacs called alveoli.
The alveoli are lined with the capillaries for the actual exchange of gases. The oxygen rich air that was just inhaled, is dissolved into the moist lining within the alveolus. The surrounding capillaries contain blood with low oxygen (O2) and high carbon dioxide (CO2). The difference in partial pressure causes the O2 to diffuse into the blood capillaries and the CO2 to diffuse out of the blood capillaries and into the alveoli. exhalation releases CO2 from the body and allows for inhalation of more oxygen.
This advanced mechanism takes place every time you breath. There are many levels of organization that must function properly in order for this whole process to work.