There are three types of fossil fuels, coal, oil, and natural gas.
Oil is made up from dead decaying animals that sank into the earth. The decaying bodies were cemented and squished together for millions of years and turned into oil. People relies on oil to keep our cars and machines working. Scientists are trying to find out ways to recycle oil.
Coal is made of cemented animal poop. It takes over a million years to turn into coal. People use coal fur heat or thermal energy. It makes energy hen it's light or burnt. coal is used to fuel trains and furnaces.
Natural gasses are used to fuel heavy duty trucks. it is also called diesel. Natural gas is pretty much liquefied gas. It is used in stoves and grills.