Imagine a snapshot of a ball sitting on an incline. If it was being held there by some imaginary force, it would stay motionless. Realistically, the ball will roll down the incline. The ball has some form of energy due to its height and unless an outside force interferes with the balls natural inclination to roll down the incline, that energy will transform form gravitational potential energy into kinetic energy.

Gravitational potential energy (GPE) is the energy an object has that depends on how far from the surface of the Earth it is. In other words, it is the energy that it has due to its vertical position. The higher the object is from the surface of the Earth, the more GPE it has. It is directly proportional to the weight (mg) of the object and its height (h).

GPE is not a vector quantity, so you can use magnitudes only for these values in problem solving. Also, h can be referenced from some reference surface, so it doesn't always have to be the surface of the Earth. It could be the height of a table or top of a building. It is important to define your reference point so if you are comparing two objects, you refer to the same reference surface.