Welcome to the TT world. We were all first time TT owners once. There is nothing mystical about RV electrical but It is unusual.
Generally the the things you really need, lights, water pump, refrigerator, water heater, and furnace run on LP and/or battery. To this you can add the radio/DVD player and antenna booster. The remainder of the items run on 120 volts.
As already mentioned if your TT has electric brakes it should have a separate dedicated line directly to the battery through a break away switch.
One thing to be aware of, is you do not know what modifications may have been made over the last twenty years to "improve" the TT. Also you may find some stop gap repairs that were to be corrected later.
All this may sound confusing but they are just part of the RV world.
Enjoy your new TT.