On the outside a single-handle faucet looks a lot like a disk faucet, but it has a narrower cylinder under the handle. Inside is a metal or plastic ball with grooves and holes. When the handle turns, the grooves or holes line up with rubber-sealed inlets in the faucet body to allow water to flow.
This type of faucet can become clogged by small particles. If water flow is slow or erratic, disassemble and clean the inlets.
Getting the parts
If water seeps out below the handle or drips out the spout, tighten the cap or the cap-adjusting ring. If that does not solve the problem, buy a rebuild kit for your model. If water seeps out the base of the faucet, replace the O-rings. If water drips from the spout, replace the seats and springs. Less commonly a ball is damaged and needs to be replaced.
Less than an hour for most repairs
Hex wrench, screwdriver
Shutting off water, dismantling a faucet, installing small parts
Shut off the water, close the sink stopper, and place a rag in the sink to catch any parts
Repair kit (including O-rings, seats, springs, and other plastic parts), perhaps a new ball