This probably repeats what was already said, but maybe it will help.
The RV has a 120V system which is powered from shore power (or generator). This system powers the 120V items such as a microwave, A/C, 120V outlets for coffee pots, TV, etc., water heater and fridge, and the converter.
The 12V system powers the slides, power tongue jack, almost all lights, vent fans, control circuits for furnace, water heater, fridge, and A/C. Furnace runs on 12V / propane. The power is supplied from the battery and/or converter and/or solar.
Propane supplies fuel to the stove, oven, furnace, and water heater and fridge in LP mode.