Atmosphere

Atmosphere is a layer of gases that surrounds planets, moons and other types of celestial bodies. Earth's atmosphere, often called air, is essential to human life, and all other Earthly life, for without it, we couldn't breathe. When Spaceships are built, they are built in such a way that they can contain the atmosphere inside that they bring from Earth or whatever world they come from.

Some alien races do not need air to breathe, in fact, Superman and other Kryptonians, as long as they are under a yellow sun, either don't need to breathe, or they can hold their breath for a long period of time.