Stain the MDF sheet by brushing a light coat of wood stain onto the top surface, wait five minutes and them wipe the stain off with a clean dry cloth.
Pour a small amount of polyurethane into a paint tray and dip a foam roller brush into it to use to apply three light coats of polyurethane to the tabletop. Allow the polyurethane to dry for 30 minutes between coats.
Turn the tabletop over so that the unfinished side is up.
Mark the folding table leg pre-drilled screw hole positions onto the bottom of the MDF with a pencil, 4 inches from the left and right sides.
Remove the legs and drill pilot holes at the marked screw positions into the MDF with a 3/4-inch drill bit in a power drill.
Reposition the legs and screw the leg assembly screws through the leg brackets into pilot holes and the MDF with a power drill.