Good evening,
I can't help you with the gauges, but there definitely should be some indicators somewhere. Often they are built into the same panel as the water pump switch. Have you found that yet?
The threaded garden hose connection is indeed your city water connection. The other one is probably to fill the fresh water tank; usually they are behind some sort of door or flap and are a capped pipe about 1" in diameter so that you can insert a hose to fill the tank. You can verify that one by opening the drain on your freshwater tank, run a little bit of water into the tank fill connection, and see if anything comes out the drain.
I do not mean to offend, but based on the questions you are asking it sounds like you could use someone to walk you through your camper and its functions. There are lots of things an experienced person could show you in a couple hours that will save you tons of time (and expense) instead of learning from trial and error. For example, speaking of water systems, there are often valve arrangements that take your water heater "off line" for the winterization process. DO NOT attempt to light your water heater before making sure that your water heater does actually have water in it, or the repairs will cost a small fortune.
The Laytons are good trailers and will serve you well if it has been taken good care of previously.
Good luck!
Regan
2003 F250XL 4WD 7.3L Crewcab LB, 6 speed; Prodigy brake controller; Big Tex grille guard/ deer deflector. Canoe hauler and camping truck extraordinaire!
2003 Layton 242 Scout- Extra batteries, solar panels, LED lighting, and propane for boondocking.