Good question! You're not the first to wonder this. In a nutshell, Training Mask is a face mask which seals around your nose and mouth. It is held in place with a neoprene sleeve around the back of your head, and a stretchy strap over the top of your head (optional).
Of the three valves in the Mask, the central valve allows you to exhale and the outer two valves provide the resistance when you breath in. The level of resistance is controlled by the valve caps, of which there are six (6). You can refer to the included instructional booklet that comes with your Training Mask 2.0 for example exercises.