Say you've got a laminated table that used to be shiny and beautiful, but now the formerly glossy surface is dull, dirty and scarred. You can buy a new table or, for a small investment and a few day's light work, refinish it. This process is not for faux wood or Formica surfaces, but rather real wood that has been varnished.
Lightly hand-buff the surface of the table, using short, fast strokes and working your way across the entire surface. Your goal is to take off the remaining gloss of the surface so your polyurethane will stick.
Thoroughly clean the dust from the tabletop. Open and stir the can of polyurethane with the paint stick. Don't shake the can or stir it vigorously, but stir slowly to avoid creating bubbles in the liquid.
Wearing your rubber gloves, dip the brush into the can and slowly spread the liquid polyurethane onto the tabletop. Work from one end to the other, with the wood grain, using long, slow strokes. If bubbles form, slowly drag the tip of the brush over them to pull them out. Allow it to dry overnight.
Apply a second coat of laminate or even a third, following the procedure you used earlier, including the light sanding.
Bubbles are the enemy. Watch out for them forming in the wet polyurethane during and immediately after application, as they will be there forever if they dry in there.
Polyurethane vapours can be harmful. Make sure the room is well-ventilated.