What energy is a potential energy?

It is the "potential (possibility) to do work". That is to say, if an object is at a certain height, when it falls it can do some work.

Both are forms of energy. Potential energy is the available energy that could be used and Kinetic energy is the energy actually being used. Think of Potential energy as being a high cliff with water...

Yes.

yes it is

The sun sends more energy to the earth every day then humans currently consume. The problem is that we are unable to capture more than a small percentage of this energy.