You remove the handle then unscrew main interior body of the faucet. You will now see a small screw on the inner end of the stem holding the washer. Remove this screw and refit the same size washer (there are dozens of sizes, you may have to get an assorted bag of washer from the store, -only about $3-4)
a washer is generally a rubber washer that tightens and seals as sometimes they will go bad and have to change it..
The rubber stop washer has failed.
When you shut the faucet off, the screw pushes a rubber washer against the opening inside the faucet and stops the water. The screw moves in and out in the handle to do this.
Depending on which type it is, it either need a new washer or seat in the valve. The washer is a flat rubber disk that seals when you turn the faucet off and the seat is a small rubber cup that does the same thing.
If you have one that won't turn off, the rubber washer has disintegrated. Take it apart and look. It is almost always the rubber washer. If you are still not sure, get the name off it and go to HD, ask for the 'repair kit' for that faucet, there will be parts and a diagram. -$5-8.
Replace rubber washers and possibly metal seats in the faucet
As in any faucet, you take it apart and replace the cartridge or the rubber seal.
Older faucets have a washer in them that seals the faucet when off. They are hard rubber and split with age. Newer ones have a small rubber cup in them that does the same thing. Either one is fairly easy to replace. Either a box of washers or a kit for the newer ones should be $3 or $4 dollars.
You take the faucet apart and replace the washer and stem seal .
Do you mean "how do I replace washer line"? They are just rubber hose from the washer fluid container to the wipers. If you have a leak, you can get a plastic splice and put it in at the split to repair.
Most of the time, the old links are corroded together, and it's much easier to use a cutting torch to remove them. Once they are removed, install new links & bushings (bolt, washer, rubber, sway bar, rubber, washer, sleeve, washer, rubber, control arm, rubber, washer, nut)
Turn main water supply off in your basement. Adjust or replace shower shut off knob.