When on battery, only the 12V side will work. Primarily this will be your lights, CO/gas detector, furnace, power lift if you have that option, water pump, 12V AUX ports. Frig if you have a 2 way or the 3 way option, roof vent fan.
120V AC power, only works when you have shore power. Items you might have, would be AC unit, outlets inside and outside the PU, battery charger. I think that might be all you have on your PU.
Have fun with your new PU