How do the various forms of energy differ?

Energy can either be "potential" energy or "kinetic" energy. Potential energy is energy that is stored in some system: a stretched rubber band, a book sitting on a table, or the chemical bonds in the wax of a candle. Kinetic energy is energy that is moving, and generally comes from the release of potential energy, such as letting go of the rubber band, the book falling off the table, or lighting the candle.