In defining kinetic molecular theory, we explained how the motion of the gas particles creates the pressure that we observe:
The pressure exerted by a gas in a container results from collisions between the gas particles and the container walls.
Each time a gas particle (molecule or atom) collides with the walls of the container, it exerts a force on the walls of the container as it bounces off (and the container exerts an equal and opposite force on the particle). This force, spread over the area of the container walls, is the gas pressure in the container. Remember – pressure is defined as force per unit area.
Based on this definition, and what we know about the motion of particles from kinetic molecular theory, we can explain the molecular source of changes in pressure resulting from changes to any other term in the Ideal Gas Law: $$P = \frac{nRT}{V}$$