Fossil fuel power plants burn carbon fuels such coal and oil to generate steam that drives large turbines that produce electricity. These plants can generate electricity reliably over long periods of time.
Oil - formed from the remains of small animals and plants that died and fell to the bottom of the sea. Their remains are covered by mud, and as the pressure increases, oil is formed.
Coal- Formed by the remains of plant life being buried under tons of sediment/rock, and eventually it becomes coal.