To understand how something works you must first take it apart to see what makes it tick. We will try to do just that -- starting with the power pack. What is the source of a star's enormous power?
The Short Answer
Stars produce power by changing mass into energy. That's right ... the solid, liquid and gasseous stuff that makes up everything you see around you is changed into energy (heat and light) inside of a star. It doesn't take much mass to make an enormous amount of energy.
Look at the jelly bean in the picture for a minute. Stare at it with awe and respect. If all the mass in this jelly bean were converted all at once into energy, it would be equivalent to 25,000 tons of TNT.
Cut this jelly bean in half and you would have the mass converted into the amount of energy in the first atomic bomb. Enough energy was released to completely destroy a small island.