Not all watches have a dial you turn to keep the device charged. Many watches are automatic and wind themselves based on the movement of your body when the watch is strapped to your wrist.
If you own an automatic watch, the need for a watch winder may be necessary if you don't always wear your watch. If your automatic watch sits idle atop your dresser or desk, it will run low on power and the timing will become out of sync or stop all together. Commercial watch winders are also extremely expensive to purchase. Building your own will save you a few dollars.
Any device can be built or rigged as a homemade watch winder. As long as the instrument you're tinkering with provides some sort of rotational movement, it can be jury-rigged into a winder. An old record player, turntable, rotisserie motor or power drill can all be fixed up to function as an automatic watch winder.
As self-winding watches are built to recharge based on your body's movements, your homemade watch winder needs to be built to imitate those movements. Winders can alternate between various speeds, change directions and shift angles to simulate different body movements. A timer can also be built in so that the winder can turn off and on automatically.