A clutch is a foot-operated mechanism used to disengage a manual transmission from the engine temporarily, while the driver is shifting between transmission gear ratios. Don't wait for a clutch to slip before doing something. The clutch also disengages the engine while the car slows down or is stopped, when the driver does not want any power transmitted to the wheels. A damaged clutch will cause damage to the transmission, because gears must be shifted while full power is still transmitted from the engine.
Clutch pedal should have 2-5 cm (3/4 to 1 1/2 in) of play. If it's excessive, the clutch may not fully disengage. If it's too little, the clutch disc and throw out bearing take extra punishment. If your car has a conventional clutch linkage, a repair manual will describe how to turn the adjuster to reset the clearance. You can lubricate the metal pivots of the clutch linkage with chassis grease, the plastic parts with silicone grease.
Many clutches are self adjusting, with tooth-pawel plastic adjusters that should periodically be lubed (on the pivot and the teeth) with silicone grease. Some self-adjusting clutches require that you periodically lift the clutch pedal up an inch or so, which isn't actually self-adjusting, but better than doing adjustments from underneath the car.
Hydraulic clutches may require not only a mechanical rod adjustment, but may also need occasional topping up of hydraulic fluid in the master cylinder, and or bleeding of excess fluid. You should replacing the hydraulics fluid in the clutch system whenever you change brake fluid, since both systems commonly use the same type of fluid.