Our lungs can breathe because there are muscles around them that pull our rig cages upward to expand our lungs (like a balloon), allowing air to enter them. These same muscles relax and compress the lungs, allowing us to breathe out again.

We actually breathe in a mixture of 78% Nitrogen and 21% oxygen, along with tiny bits of argon, carbon dioxide, water, and other gases. When we breathe in, our diaphragm (a muscle that separates your upper and lower body) contracts, which makes it move downward. As it moves down, it expands the lungs, pulling in air. Oxygen enters through the membrane of the alveoli, which then travels through the blood to the rest of our body!

Lungs have lots of surface area to exchange gasses with the air, mainly oxygen and carbon dioxide, although a lot of water vapor also escapes as a side effect.