Nice camper. I don't know if it came from the factory that way, or if previous owners did some mods.
On the left side, nearest the front, that looks like the water fill inlet to the fresh water tank.
The next one back, under the window, is the sink drain. (I connect a hose and run it to a gray water jug in my truck bed).
Lastly, you have the "city" water connection. If you are in a campground with water hookups, you connect the hose here. Fresh water runs directly to the kitchen sink, bypassing your other tanks and lines.
You can test and verify all this at home. Good luck.