Usually "City Water" connection means for a hose. You use a drinking water-rated hose (usually white, maybe blue) connected to the supply via a pressure regulator then to the CW fitting on the coach.
"Gravity Fill" connection means a separate filler where you direct the stream of a hose into it to fill the tank. The male end of a hose (again DW-rated) will fit into that connector and there should be a vent plug to let air escape as water goes in. No need for a regulator to fill a tank with a GF.
Our first coach had CW and GW fittings. Present one has only the CW type and a valve to direct water into the fresh water tank.