Like mentioned you can heat with propane and/or with electric. On my trailer the Water Heater switch inside the trailer is to turn on the propane.
For the electric there is a switch on the water heater itself. Open the cover on the outside of the trailer and look for that switch. They often break and people end up running wire to the inside of the trailer. So that you can turn on the electric element without going outside.
There is also a breaker for the water heater to run in electric mode.