Cut four rectangles out of 1/2-inch plywood with a saw. The plywood should be of high quality and free of any knots or other imperfections.
Sand the entire surface of all four rectangles with 80-grit sandpaper, then again with 120-grit sandpaper. An electric sander will greatly speed this process, but you can do it by hand as well.
Brush two coats of primer onto each rectangle, allowing each coat to dry completely. Then brush on two coats of paint in the color of your choice.
Lay two of the rectangles on the floor next to each other, with their long edges touching.
Place three small hinges over the joint between the rectangles, spaced out evenly across the joint. Screw them to the wood with the screws included in the package. If these screws are longer than 1/2-inch, use your own screws to prevent them from piercing the other side of the wood.
Repeat this process with the other two rectangles.
Place both hinged pieces on the floor hinge-side down, with their long sides touching. Attach three more hinges the same way you did the previous ones, making a divider that can fold up like an accordion.