Here's why:
* Pressure is defined as the force applied perpendicular to a surface divided by the area over which that force is distributed.
* The more force you "put on" a surface, the higher the pressure.
* The larger the area over which the force is distributed, the lower the pressure.
Example:
Imagine you're standing on the ground. Your weight is a force acting on the ground. However, the pressure you exert on the ground is determined by how much force you apply (your weight) and the area of your feet. If you stand on one foot, the pressure is higher than if you stand on both feet.
Let me know if you have any other questions!