What is the difference between force and pressure?

The way I would explain it is that the two are closely related but that pressure depends on how much of an area the force is being exerted upon.

To find force, you have to know the mass of the object and its acceleration.  Once you know that, you have the force because Force = mass times acceleration.

To convert force into pressure, you have to know how much of an area the force is acting upon.  Stated mathematically, P = F/A where P is the pressure, F is the force, and A is the area.

So the identical amount of force exerts a lot of pressure on a small area or a little pressure on a large area.  This is why you wouldn't want to sit on one nail but you could lie on a bed of nails.