The simplest puppet theaters are screens that hide the performers, with an opening at the top where the puppets emerge. These are usable, but a stage with a curtain the puppets can perform in front of while the performers are standing or seated is much easier. A folding stage, with a curtain, can be made from a single sheet of heavy plywood and a piece of piano hinge. The plywood is light enough to move easily, but heavy enough to stand without a frame.
Use a table saw to saw a 24-inch length from each end of a sheet of 3/4-inch-thick plywood, creating two 24-by-48-inch pieces and one 48-by-48-inch piece.
Use a drywall square to draw a rectangle 18 by 36 inches, centered in the 48-by-48 inch piece of the plywood. Drill a hole in one corner of the rectangle with a 1-inch paddle bit.
Start a jigsaw inside the 1-inch hole and cut out the rectangle.
Sand the three plywood panels with 100-grit sandpaper on a random-orbit sander. Concentrate on the edges, removing any splinters.
Cut a 96 inch piece of piano hinge in half with a hacksaw to create two 48-inch long hinges. Lay the three plywood panels down flat. Fit one 24-by-48-inch piece against the side of the 48-by-48 inch panel, with the rectangle opening toward the top and the smaller panel on the right edge, with its 48 inch edge aligned to the larger panel.
Attach the hinge along this joint, face mounted, using one 1/2-inch wood screw in each hole. Use a cordless drill to drive the screws. Fit the remaining 24-by-48-inch panel against the other side of the larger panel and attach it using the remaining hinge, face mounted with one 1/2-inch screw in each hole.
Stand the stage upright with the two smaller wing panels, standing at right angles to the larger stage panel, supporting it.
Cut out a 20-by-46-inch piece of sheer black polyester fabric. Staple one long edge of it along the top of the stage opening on the hinged side of the panel, 1/2 inch above the edge, using 1/2-inch narrow crown staples from an air stapler, one every 3 inches.