Direction: Work is to be done against a body to take it from the standard position or shape to any other position or shape. This work remains stored in the body as potential energy. While coming back to its original position the body can do work, so potential energy of the body decreases and becomes zero when it reaches to its standard position. At this stage the body does not do any work.
The statement is generally made that the zero of gravitational potential energy is the exterior of the earth and that the potential energy is comparative to the height above the earth’s surface. This is an estimate which is only applicable near the surface of the earth, but is well for baseballs and other familiar applications of gravitational potential energy. If you are in a room, it is rational to just call the floor the zero of gravitational potential energy, and calculate the energy of an elevated object with respect to the floor.