The water pump sucks water from the tank and pressurizes the bus plumbing lines running to faucets, etc. Run a line from the bottom port in the tank to the inlet side of the pump. Usually there is a strainer on the inlet side. The pump monitors pressure on the output side and will come on automatically when pressure drops when a faucet is opened.
I used PEX to plumb in my Atwood 6 gal. water heater.
Think about how you will drain your water system when installing the water lines so they can be fully drained for winter storage. Many use compressed air to blow the lines dry but I don't have a compressor so I ran my lines so that they naturally drain back into the holding tank and water heater. Then I use a shop vac to suck the water heater dry.