Fossil fuels are natural fuels formed in the geological past from the remains of living organisms. Step 1: Over millions of years, the remains of plants and animals were buried under layers of sediment and rock. Step 2: Intense heat and pressure transformed these organic materials into carbon-rich substances. Step 3: The primary types of fossil fuels are coal, petroleum (oil), and natural gas. Step 4: These fuels are extracted from the Earth and burned to release energy, primarily for electricity generation and transportation.