If you are talking about the propane furnace, it needs Propane and 12V DC electrical. The electric runs the blower fan, the computer board and igniter.
Some RV's will have either a heat pump system or simple electric heating coils in the air conditioner. Those will run on 120V AC and you will need to be hooked up to shore power (or have a generator).
Alternatively, you may have a small fireplace or wall mounted electric heater which again will run on 120V AC.
The fridge can typically run on propane (with 12V DC for the controls) or on 120V AC electric. Some will alo run on 12V DC but then you need a big battery bank and a way to charge it.
Lights and water pump are typically 12V DC.
Jacks & slideouts are 12V DC.
Everything running thru the household style outlets are 120V AC.
