Ever watched a blacksmith making a horseshoe (or anything else)? If you have, you’ll know that just burning wood or coal in the forge (the fiery pit that heats the metal) is not enough; you’ll see the smithy also blow extra air on the fire via a set of bellows (or a converted leaf-blower these days).
The extra air means the fuel burns faster and hotter and is able to get the metal hot enough to soften and be workable. This principle is also why bushfires burn hotter and more destructively on windy days. A turbocharger uses precisely the same principle.
A turbo blows extra air into a car’s engine, allowing the engine to burn more fuel. More fuel equals bigger bang, bigger bang means more power to the wheels. The clever thing about a turbocharger is that it uses the engine’s by-product – the flow of exhaust gas (part of the turbocharger is mounted inside the exhaust pipe where the gasses spin it like a waterwheel in a river) – to spin it and make it pump that extra air.
In the old days, the downside was that there was usually a delay between when you floored the throttle and the exhaust gas started rushing by and spinning the turbocharger. But modern engine management and smaller, lighter turbochargers have reduced that delay (called lag) and now turbo engines are hugely responsive. And because they only help burn more fuel when you want more power, the rest of the time they don’t increase fuel consumption at all.