You could google it and it will give you some information but I don't know if it's what you are looking for.
The Booster is actually a brake assist. It connects to vacuum on the engine. There is a diaphragm inside the booster can. When you step on the brake pedal. The booster (working from the engine vacuum) helps add pressure out to the wheel cylinders. Another way to think of it is that it is actually a multiplier of the pressure which is applied from the master cylinder due to the action of you stepping on the brake pedal.
Sometimes when guys put a larger lift cam in their engines the engine develops less vacuum thereby causing the brake to be harder (it acts more like a manual brake rather than a power brake). There are booster pumps available (usually at speed shops or online at the high performance sites like Speedway or Summit)
