1st time trailer owner, question regarding battery/power

There is no switch. You plug it in and providing the converter is working properly, you should have 120V & 12V to all facilities. When unplugged, you will have no 120V so therefore the microwave, Air Cond., and any other 120V appliances won't work. However all your 12V appliances like lights, water pump, refrigerator, etc. will work until the battery dies. Note, your fridge and furnace will work on propane with electronics powered by 12V; but the furnace fan will rapidly deplete your battery.