A shaving horse is essentially a clamp that you sit on that will respond to the force you apply, which clamps the wood in place. This allows you to use a draw knife to safely shape the wood.
Sitting on the “bed” supported by three legs, your feet push an arm away from you that through a pivot will clamp the wood to the top of the horse. Then using draw knife you pull towards yourself shaving the billet into the shape required, quite often a perfect cylindrical blank for the pole lathe.
The beauty of the device is that the harder you need to pull with the drawknife the harder you must push with your feet, the clamp therefore acts automatically and requires little or no thought. It is a simple matter to frequently release and turn the piece working evenly around it and flipping it over to work along the complete length.
I can safely say that everyone I have known to use a shaving horse has been charmed and enthralled by the simplicity and effectiveness of this ancient tool. It is possible, as I often do, to finish components on the shaving horse alone using drawknife and spokeshave (imaging a very small drawknife in a wooden or metal housing).
Generally though the process described above are in preparation for turning on the pole lathe and we now have a straight cylindrical “blank” ready for the final stage of shaping.