The water system is capable of being operated in 3 different ways.
The first is when you attach a garden hose to the city-inlet connection and you then turn the water spigot on at the source. The water will pressurize inside the camper water lines and work just like they would in your house. When you use the water this way, you want to make sure the on-board water pump is turned off.
The second way to use the water system in your camper is when you are not hooked up to a water source. In this situation, you fill your fresh water tank, where and when you do have available water. Depending on hour your camper is designed, you may fill the fresh water tank by sticking the garden hose in a fill port. This is called "gravity fed".
Other systems require the garden hose to be connected to the fill port but there is a valve that flips from "fill" to "run" or something like that. In this situation, flip the valve to "fill" to fill the fresh water tank. When filled, flip it back.
Then you need to turn on the 12 volt on-board water pump and pressurize the water lines. Then leave the pump turned on all the time. It will cycle (turn on and off), only when you turn a water faucet on.
The third way to use the water system is when you winterize the water lines so they won't freeze in the winter. There will be a separate hose, or a separate place to connect a hose that is stuck in a bottle of RV anti-freeze and sucked out of the bottle to displace any water in the lines with RV antifreeze.
In the process of getting things set up, you will also need to make sure the water heater is filled with water BEFORE turning it on. If the tank is empty and you turn it on with electricity, it only takes about 5 seconds for the heating element to burn out. If empty on gas, it could burn out the thermostat.
There are multiple videos on YouTube that will explain how to hook up the water, how to run your on-board, and a bunch of other things that will help you. YouTube is your friend.
And congrats on that new camper!
2019 Montana High Country 375FL Fifth Wheel
2014 Chevy Duramax HD 6.6 - 3500 Diesel Dully Long bed Crew Cab