There are three major types of fossil fuels.
There are three major types of : coal natural gas and oil. All are formed over millions of years.Over time the material is compacted in the Earth and heated and the material turns to coal natural gas or oil.
Coal is a solid form of ancient decayed land vegetation.
Natural gas is a gaseous form of fossil fuel. Many scientists believe natural gas is the remains of marine micro-organisms. Natural gas is made up of methane.
Oil is a liquid fossil fuel. It is also the remnants of marine micro-organisms that died millions of years ago.
To learn more check out this page from NASA.