Energy is everywhere and it's what makes everything move. All work happens because of energy, and as long as we live, our bodies produce energy. There are two types of energy: potential (or stored) and kinetic (in motion). The sun is the ultimate source of all the energy there is on the earth, through one or another ways. It's stored in fossil fuels and plants, the wind and water. Some forms of energy are heat, sound, electricity, light, and falling things. And it's able to change forms.
Bill Nye the Science Guy did a great job explaining the basics of energy. Take a look!