The switch to connect the House-battery to the 12v circuit is usually on the monitor panel (water tank level, battery level, propane level). The switch might be marked: power, aux., battery. If button is pushed up the panel should work, along with 12v lights, etc.
On some RV's the panel may work when plugged in, BUT; the house-battery will not charge if not connected to the 12v circuit.
Test the 120v, ac, outlet you plug the RV into by plugging in a lamp, hair-drier, etc., to see if it is working. If yes, plug the RV cord into it and you should find the outlets working in the RV, along with the microwave. If not check the circuit breaker in the house.
Other items like furnace, air-conditioner, 12v lights, need a battery connected and/or a working converter/charger. Thermostats are 12v powered.