Another Newbie with 0 Knowledge about RVing

There is almost no standardization in various brands and models of motorhomes. Your questions may seem basic, but correct answers, not guesses, are often technical and require you to do electrical and other tests and adjustments that are probably beyond your experience. I would guess that your fridge needs serious electro-mechanical work or the previous owner would have had it working on AC power. There are generic motorhome operation and maintenance books that can help you become familiar with the various 12volt DC, 110volt AC, propane, plumbing and holding tank systems, including fuse and breaker boxes, control panels and switches. I think that you would do best to find a good friendly mobile RV repair guy to show you how to locate and operate things and at the same time diagnose things that are not working properly and fix them. There are not many repairs, replacements or upgrades that you can do yourself at this point. You will eventually need to learn how to check battery voltages, electrolyte levels, clean terminals and connections, etc. Do not try to run the roof AC unit and/or microwave when plugged into an outlet in your garage unless is is rated for 30 amps and you are using a heavy duty shore cable extension. Low voltage can damage your air conditioner. Don't run your fridge unless your rig is nearly dead level, off-level operation can damage the cooling unit. Good luck getting your rig ready for full enjoyment. Make sure your tires, brakes, and engine cooling system are good. RV tires go bad/become failure prone, sitting parked for five years even though they may look like new. Expect to spend some money getting your rig reliable and enjoyable for any
kind of touring and camping you ask of it.