Oil is one type of fossil fuel. A thick, gooey, black liquid, oil is also called petroleum. Natural gas is another kind of fossil fuel. Normally you can't see or smell natural gas. Coal is also a fossil fuel.
Coal comes in many forms ranging from hard, black colored rocks to soft brown dirt.
Some coal burns hotter and cleaner than other types of coal. Since all these fossil fuels formed in the ground, they first have to be taken out of the ground to be used. This process is different for each fuel. To find oil and natural gas, machinery drills through the surface or crust of the earth. Oil and natural gas are found between layers of rock.