Question

You know that energy cannot be created or destroyed, so what happens to it?

Answer 1

Mass cannot be created nor destroyed as well.

So, energy just goes into other things. 

Example: you are born. You have carbon dioxide in your body, (or star dust). When you die, your body releases that gas.

Make sense?

I hope this helps! (:

Answer 2

Energy is converted. For example, stored CHEMICAL energy in a match head is converted into HEAT energy and LIGHT energy