Glad to meet you. Looks like you're off to a grand start. My 2011 model doesn't have a switch under the sink but from reading around the forum, I think it's the water pump switch. It's in a really inconvenient place in my unit but was evidently relocated to the sink area--where it belongs, IMO.
If your water lines are full, nothing much should happen when you flip the switch. The pump shuts off when there's no outlet for the pressure. There may be a short burp from the pump when you first turn it on as it ensures the lines are full. Always travel with the switch off so that the pump doesn't come on while you're not in a position to notice it. The pump can run dry for a short time without damage, in case that should happen. It will get hot, though, besides sucking your battery down.
I'll let folks who have newer models confirm whether that's the water pump switch or not. Your dealer dropped the ball if he didn't orient you on the switches and valves, the converter, the water heater, the Cool Cat, the furnace, the fridge, and so on. My suggestion is to stop by the dealership and have them give you a thorough orientation.
It's never too late to have a happy childhood!
Lee, WU0V, and Courtenay, N0ZDT
2011 Rockwood A128
2000 Silverado 1500 pickup
60W solar system
2000W inverter generator