Gears are multipliers. A clutch is basically two spinning plates - one on the gearbox/transmission, one on the engine.

When you press the clutch pedal in, it moves the plates apart so they don't touch. When you let the pedal out, the plates move together, slip and rub for a bit, and then grab.

While they are all the way apart or all the way grabbed, they don't wear. While you are in between, they are rubbing and wearing, and trying to get the engine/transmission to spin the same speed.