Law of Conservation of energy states that total energy of an isolated system remains constant or conserved i.e. it can neither be created nor destroyed. It can only change from one form to another.

For example, the total energy of a ball at a height will remain same to when it will be at ground where some potential energy is converted into kinetic energy and a little energy is converted into heat energy but it is negligible. Same goes in tyre running where some energy is used as friction.

More info on the topic can be read from : https://en.wikipedia.org/wiki/Conservation_of_energy