Sand the coffee table down to the bare wood, using an electric orbital sander or sandpaper. Wear safety goggles to protect your eyes.
Wipe down all surfaces of the table to remove residual wood dust.
Spread a thick layer of old newspapers on the ground or in the garage. Place the table on the papers.
Stain the table, if desired, using the paintbrush. Apply the stain in even strokes, painting in the direction of the wood grain. Let the piece dry for 24 hours.
Shake a can of polyurethane vigorously for one minute to mix thoroughly. Hold the can 12 inches over the surface of the coffee table, and spray from side to side in an even coat. Cover the entire table and the legs. Let the piece dry at least 12 hours.
Buff the coffee table when it's dry. Apply a second polyurethane coat, and allow to dry. You can apply a third or fourth coat to achieve a pleasing finish. Buff the table between coats.