This is the easiest system to understand. A key is used to directly interact with the centre wheel , to set the time, or the winding mechanism. The pictures below are taken from the George Oram & Son 8947.
The centre key hole is for time setting, the one above and to the left is to wind the mainspring barrel
With the 3/4 plate removed, you can see that at the centre the key moves the centre wheel while above it winds the fusée, which in turn winds the mainspring barrel
One interesting feature is that the click is on the dial side
Lever set mechanism
The video and pictures below are from a Progress 6s pocket watch.
The setting lever and the setting mechanism. Note that either the right-hand wheel interacts with the minute wheel or the left-hand wheel interacts with the ratchet wheel.
The three wheels turn around pivots that are on the underside of the setting mechanism cover, allowing them to slide on the main plate.
The three wheels taken off the setting mechanism cover
Another type of lever set mechanism only uses the lever to reproduce the pulling out of the crown, but otherwise uses the standard stem-based mechanism for the actual winding and setting. The pictures below are from an Elgin Model 7 Grade 594.
The lever setting mechanism only moves the sliding pinion on the stem, it does not move any wheels
Focus on the lever setting mechanism
From the other side, the stem with its winding and sliding pinions is similar to what can be found in modern watches
Crown set mechanism
The mechanism with a sliding and a winding pinion on a stem is what can now be found in almost all modern watches. It is illustrated with an ETA/Peseux 7001.
Dial side and keyless works
The mechanism in the winding position with the sliding pinion interacting with the winding pinion
The mechanism in the setting position, with the sliding pinion interacting with the intermediate wheel
