Diagnosis
The drain pump is either clogged or dead. A small object like a sock, coin, or bra wire can jam the impeller, or the pump motor can burn out from the strain.
How to Fix It
Unplug the washer. Access is through the lower front panel. There are two clips on the bottom edge—push in on them and pull the panel toward you. You'll see the drain pump at the bottom center with a hose going to it. Place a shallow pan underneath. Disconnect the drain hose clamp and the wire connector. Remove the pump (usually a couple of screws). Check the impeller inside—you should be able to spin it freely by hand. If it's stuck, clear the debris. If it spins rough or not at all, the pump (part number like WPW10749474) needs replacing.
If That Didn't Work
If the pump hums but doesn't move water, the impeller might be broken off its shaft internally. You'll need a new pump. Also, check the drain hose itself for a kink or blockage all the way to the standpipe.
Heads Up
When you reconnect the drain hose to the new pump, double-clamp it. Those spring clamps can lose tension. A small worm-gear hose clamp over the factory one adds insurance against a leak.