If you are plugged in at a campground turn it to electric. If not open you propane bottle turn on the stove and light it. Once lit. Turn off then turn the fridge switch to propane. The reason to light the stove is to bleed the lines of air which will help when trying to light the fridge or hot water heater on propane
2015 Redwood 36RL pushing a 2015 Denali DRW
On ours, we leave it on Auto. "on" means on AC. If we lose AC, and it goes to propane, "gas" also lights. If we intentionally switch it from auto to gas, (to save AC, say 20 amp service) then "on" and "gas" are both on.
The lp should be turned off only if the RV is indoors like in a garage or parked in front of a gas station. This is to prevent asphyxiation, but you can turn it on any other time. You should be more concerned about your rig level. RV refrigerators will not cool unless they have a proper level. If the rig level is proper then the solution(consisting of sodium chromate,ammonia,hydrogen and water) inside the cooling unit percolates, this is how the heat gets transferred from out of the refrigerator. I bought a fridge from Best Brand Appliance Premium Home & Kitchen Appliances Store Vaughan, Toronto | Best Brand Appliance a few years back but I had it running on an extension chord.