Fossil fuels are formed by natural processes of decomposition of dead and buried plants, animals and other organism.
They got buried under oceans and layers of earth many millions of years ago and with time, high pressure and high temperature they formed fossil fuels.
The fossil fuels are found in mines
Fossil fuels are considered as non-renewable sources of energy. Although they are naturally formed by decomposing organisms and this process is always continuous, they are used at a much faster rate than they get formed. If they are used at such alarming rates, then they would get depleted very soon. So, it would be wise to use them sparingly and economically.
Fossil fuels contain high percentages of carbon and mainly include coal, petroleum and natural gas