How is the pressure exerted by the gas on a unit area equal to that of pressure experienced by gas

Since particles of gases move in every possible direction, they continuously collide with other particles and also with the walls of a container. 

When the particles hit the wall on a unit area, they exert an unbalanced force on the wall of a container. This force, when divided by area, gives to pressure. 
or, The pressure a gas exerts on the walls of a container is the collective force collisions of the gas molecules exert on the container walls, per unit of surface area. Pressure is a measurement of force/unit area.