Can this be used for a ceiling light fixture? No receptacle to plug it in.

No, you must plug a lamp or similar item into the controller that plugs into the wall. That is what the remote switch is controlling, the plugged in part.

You need to find the wire that feeds the fixture, disconnect it from the live feed and attach a plug to it. I did this with the wire that feeds my backyard lights and it has worked fine for a couple of years. Caution- do not attempt this unless you are sure of what you're doing, electricity can injure or kill.