Sand the top, bottom and four sides of the plywood until smooth. Wear goggles and gloves for protection.
Prop the piece of plywood on sawhorses in a well-ventilated area or outside.
Apply wood stain or a coat of primer, if you plan to paint, to the top, bottom and sides of the plywood. Allow it to dry overnight.
Paint the plywood. Apply one coat and allow it to dry overnight before applying a second coat of stain. Let the paint or stain dry overnight.
Turn the plywood so that you have what will be its bottom facing up. Position the four leg plates at each corner. Attach the leg plates to the plywood by drilling screws into the holes on the plates.
Attach the legs to the table by screwing into the leg plates. Usually, table legs have a small threaded bit sticking out of the top that you simply screw into the opening of leg plates.