what is energy and use the electromagnetic spectrum to explain it.

Energy = Planck's constant x frequency.

Thus, those frequencies that are very low have lower energy than those that are high. High frequencies are gamma rays and x-rays, lower are ultraviolet light, visible light, infrared radiation, microwaves, radio and TV, etc.
Here is a web site that you can read more about it.
http://en.wikipedia.org/wiki/Electromagnetic_spectrum