Here's a breakdown:

* Other air molecules: Air is constantly in motion, and the molecules are constantly colliding with each other. These collisions are what create air pressure.

* Surfaces: When air molecules hit a solid surface, they bounce off in a different direction. This is how air pressure is exerted on objects. Think about the wind pushing against a sail.

* Other particles: Air also contains particles like dust, pollen, and water droplets. These particles can also cause air molecules to bounce off them.

The more collisions there are, the higher the pressure. This is why air pressure is higher at sea level than on top of a mountain (there's more air above to press down).