Breathing is basically the process of moving air into and out of the lungs.
Breathing is accomplished by manipulating the pressure gradient between the surrounding atmosphere and the thoracic cavity.
For all practical purposes, the pressure of the surrounding atmosphere can be considered a constant.
Thus, the desired pressure gradients are achieved by changing the pressure within the thoracic cavity.
The pressure in the thoracic cavity alternates so that it is less and then greater than the pressure of the surrounding atmosphere.
The two types of human breathing are costal and diaphragmatic. They may be used individually and independently, or they may be used in combination.