Wood is bent by cutting thin strips—most often between 1/16 to 1/8 inches thick. It is then shaped by either steam and then placed into a form that has the desired shape, or the thin strips can be placed directly into the form without steaming them.
I have made a few items by using a form. The desired shape is first drawn onto a thin template (I use 1/4” MDF—medium density fiberboard) and then cut out of that piece and then traced onto thicker MDF, usually 3/4 of an inch. Depending on the width of the piece, several layers of MDF are glued and screwed together. All of them are smoothed along the edge by use of a router and/or a spindle sander.
After the form is complete and the thin strips of wood called laminations are cut, they are glued together and clamped into the form for at least 24 hours. It is quite an interesting process. If the piece is wide, say more than 3," the laminations need to be clamped from both sides. This calls for many clamps, perhaps 40-50 if the piece is long.
Generally, two people are necessary for this procedure, as there is only some much time to glue all the laminations and clamp them into the form before the glue sets.
For guitar making, there is a special steam bending tool designed for guitars. The steamed pieces are placed into a form designed specifically for guitar bodies. We have this equipment at the college where I work.