Unscrew the light bulb in the garage door opener. Screw in a light bulb converter with a plug-in feature. With some converters you can have both an outlet and a screw-in for the bulb.
Move a stud finder along the ceiling behind the garage door opener to find the ceiling joists. Mark the location of each joist.
Hold the fluorescent lamp housing against the ceiling and perpendicular to the joists. Screw the housing into the joists using the mounting holes in the housing and long wood screws. Use a screwdriver to tighten the screws. Attach the lamp to at least two ceiling joists using two screws at each joist.
Insert the light bulbs. Attach the lamp shade plastic. Insert the plug end of the wire into the plug-in on the light bulb adapter. Make sure your wires aren't dangling; they can be bundled with a twist tie.