Two configurations: side sprayer (separate hose and head) and pull-out/pull-down (built into the spout). Side sprayers use a diverter valve to redirect water -- sticks, clogs, or fails and the sprayer gets nothing even though the faucet works. Pull-out/pull-down: no diverter, water flows through the hose at all times. Common failures are clogged head, kinked hose, or failed check valve. Both types: straightforward, inexpensive repair.