The atmosphere is what we call the whole bunch of air which surrounds the Earth.
A basic problem with understanding aeroplanes and flying is understanding that air is real stuff! It is invisible, so it looks like a plane is flying though nothing. This is not true!
Air is just as real as metal, wood and concrete!
In aviation we rely on air being real to fly. The wings push the air downwards giving the LIFT that holds the plane up.
Note: There are two different ideas about how this works… the deflect the air downwards theory and the the Bernoulli Effect. Even after more than a hundred years of flight there is still debate about which is correct! What nobody argues about is that it is the AIR that allows the wing to provide the LIFT we need.
We also need air to breathe… that’s as real as it gets!