The Fuel which is made naturally by decomposing of dead and buried organisms are called Fossil fuels.
They are not man-made and are a non-renewable source of energy.
The dead part of animals and plants are subjected to high temperature and pressure from Earth's crust and then fossil fuels are formed.
We have to use it wisely as it takes a lot of time to be formed.
There are three major fossil fuels:
Fossil fuels can be found easily are cheap but they produce a lot of carbon dioxide which is not good for the environment.