Power went out. The shower was on and all the water was used. Power is back on. Pump will not turn on. I believe I have to prime the pump, but don't know where to find the "impeller housing."

Is this a well pump or what?

The impeller housing is where the water comes in and out of the pump. There should be a separate fitting on the pump by the water inlet (on top of impeller housing) you can remove the fitting to pour water in and help "prime" the pump. I find it is helpful to install a threaded ball valve here for future use. It may take several gallons of water (5 or more) to do so. Here is a link for diagram of a jet pump. Part 3A is where the pump is primed. You may need to replace the check valve also.
http://www.searspartsdirect.com/partsdirect/part-model/Craftsman-Parts/All-Products-Parts/Model-3902518/0247/1050000/P0411099/00001

RJ