Layer 1: Troposphere
The lowest layer of the atmosphere is called the troposphere. It is in contact with the ground. The layers on top of it compress the air within this layer, so most air molecules are near the ground.
We live and breathe in the troposphere, which extends from the ground to about 10 km above the ground. What you see from an airplane window is the troposphere.
Most weather is confined to the troposphere as well (although some cumulonibmus clouds reach the stratosphere).