use a washer..
Two handle, if the handle turns a full circle, it uses a washer. Either flat or beveled. If it is a quarter turn or a single handle, it uses a cup and spring. Either is easy to fix. Turn the water off. Remove the handle. There should be a cap on the top that pops off and a screw underneath. Take the screw out and remove the handle. There is a nut holding the stem down. Take that off and the full turn faucet unscrews out of the hole, the quarter turn pulls straight up. If it unscrews, the washer is on the bottom of the stem, held on with a screw. If it pull out, the cup and spring is in the bottom of the hole. Remove and replace with new. Make sure the cup is in the hole all the way around. Reassemble and the leak should be fixed. With the quarter turn faucets, there are O rings in the handle that should be changed at the same time. There should be a repair kit available for most faucet brands that has all the right pieces. $4-$6
You would be better served by buying a new one.
bob...
Unscrew it counterclockwise from the faucet and clean out the rust physically or chemically from the wire screen.
A faucet aerator is usually attached to the end of a faucet.
You can put an aerator wherever there is threading for one.--I'm not sure of your description "brass faucet valve". - The end of the spout is generally threaded for an aerator.
Female x Female coupling
At the very tip of the spout.
A clogged aerator on the end of the faucet would cause the water flow to decrease in that faucet.
Normally at the end of the faucet spout
Unscrew the aerator and clean it and reinstall it
Probably a clogged aerator. Remove the aerator and clean out the screen and reinstall.
Clean the aerator
Mineral deposits; most are formed in your pipes when water is not flowing. The aerator can be removed and cleaned extending the life of the aerator. The aerator will eventually deteriorate and should be replaced. Depending on your water supply and the pipes, the minerals can be several different colors.
well if you have a plugged aerator or your water line is corroded then that is usually the reason a faucet has low pressure if its just one faucet.
You need a special adaptor to link the two. This is an insert, threaded at one end to fit where the faucet aerator fits (you remove the aerator) and at the other end a pipe thread to fit a shower hose. These are commonly available in most plumbing stores and there are 2-3 variations. -Take your aerator along for comparison when buying the adaptor.