We have seen that moving objects posess kinetic energy.  Objects may also posess energy just because of where they are, like an apple in a tree.  While hanging there, the apple is motionless, so has no KE, but if you were under the apple when it fell, it would do work on your head!
This means that the apple had energy due only to its position.  This is called gravitational potential energy.

There are other types of potential energy, like the chemical potential energy stored in gasoline, electrical potential energy, and others.

Gravitational PE is given by mgh.  PE = mgh. Of course, soving this equation yields an answer in Joules.  Also remember that near Earth's surface we use g = 9.8m/s/s.