The fact that they are under the influence of the gravitational field gives objects the capacity to fall.  Remember the exploitation of waterfalls to generate electric energy.

In the following visual we will discover gravitational potential energy and the way to calculate it:

LEARN: Gravitational potential energy is due to the capacity of objects to fall.  Its source is the existence of the earth's gravitational field.  Its magnitude is directly proportional to the height at which the object is found, with respect to a determined reference point which we situate on the surface of the earth, and the mass of the object. Its mathematical expression is: