Once fossil fuels are extracted and refined, they are ready for use by common man. When combustion takes place, the hydrocarbons present in the fossil fuel creates energy. The heat that is used to burn fossil fuels cause molecules of carbon and hydrogen to react and produce large amount of energy. The formation of this new energy is used by us for various purposes. For example: when you put fuel in your car, the engine burns the fuel and converts the energy produced by burning of fossil fuel to mechanical energy which results in movement of vehicle forward. When fossil fuels are burnt, it releases carbon and hydrogen molecules to react and produce high amount of energy and heat.
The chemicals present in the fossil fuel react only when they come in contact with other heat sources. When they are exposed to heat, the hydrocarbon chain converts the heat energy contained in the fossil fuel to electrical energy to create electricity or mechanical energy to drive the engines. Coal power stations uses similar feature. They burn large amount of coal and used the heat produced by them to activate generators which in turn produce electricity.