The tank itself does not push air to you. You create the flow by breathing in, which opens a small valve inside the regulator. When you exhale, the used gas leaves through one-way ports and rises as bubbles to the surface. Most recreational divers use compressed air, but enriched air nitrox and other gas blends are also common. No matter what mix is inside, the idea is the same: store gas safely, reduce its pressure to a breathable level, and deliver it smoothly when you ask for it.