Turbocharger - Everyone knows a turbo gives you more oomph, but how does it do it?
As explained under Cylinders, an engine burns fuel and air in each cylinder. A turbocharger compresses the air before forcing it into the cylinder, so increasing the amount of oxygen available to mix with the fuel.
This gives a more powerful and efficient burn, and so more power and economy. The spinning of the turbo itself is driven by the engine's exhaust gases. (See Supercharger and Intercooler).