Energy is usually defined as "the capacity to do work" but just what does that mean? Work is defined in physics as the exertion of a force over some distance, e.g., lifting a rock up against the gravity of the Earth. You probably have a pretty good colloquial grasp of the idea of "work" as something that takes effort. Energy is also something that is conserved within a closed system. This means that it is neither created nor destroyed but simply moved about (possibly changing from one form of energy to another). Light is basically a form of energy, one that radiates through space. So the Sun can release nuclear energy, creating light which travels through space to the Earth, where it can be absorbed by, say, a photocell, which in turn permits a motor to run propelling a solar-powered car forward.