A car’s engine, if you want to get right down to it, is nothing more than a pump. It draws in air and fuel, burns it (which is where the power is made) and then expels what’s left. The efficiency of any engine is directly related to how well it takes unburnt fuel and air in, and how well it gets rid of the burnt left-overs – in other words: how well it breathes.
To increase that efficiency, a supercharger (itself a pump, if you want the truth) pressurises the air going in to the engine, forcing it down the engine’s throat. That means more fuel can go in at the same time as that extra air and there’s a bigger bang. Bigger bang equals more power. Think of it this way if it helps; what do you do when your campfire won’t burn properly? Yep, you blow on it. You become the supercharger. It’s the same process in your car’s supercharged engine.
There are different types of supercharger, but the important thing to know is that they’re powered by the car’s engine, usually by a rubber belt. That means they consume a certain percentage of the engine’s power, but the gain they provide makes up for that and then some.
Talk about a symbiotic relationship!
Now read about what RPM means.