Place a closed refrigerator box on its short side so it stands tall. Cut off one side of the box so you can access the inside of the box. Hang a black sheet over the cut back of the box and secure it to the top of the box with thumb tacks so you can pull it aside to access the stage.
Cut a square into the side of the box opposite of the side with the black sheet. Make the square the size you want for your puppet stage and place it two-thirds of the way up the box. This gives you enough room to duck under the open part of the stage while still operating the puppets.
Hang two pieces of red fabric over the open square on the front of the puppet stage using thumbtacks. Position the cloth pieces so the seam where the cloths meet runs down the middle of the open stage. When the play begins, pull the cloth back and pin it to either side of the stage.
Reach through the sheet at the back of the stage and set heavy weights on the closed flaps at the bottom of the box. This makes it difficult to tip over easily. Set down cushions over the weights to protect your legs when you sit inside the box.