First make sure there is water in the hot water heater. Turn on the electric with no water and it will burn out in seconds. Most rvs have a bypass for winterizing and you drain it for winter.
Once you are sure it's filled, you can use electric or propane. For electric make sure the breaker is on and then turn the outside switch on. In about 20min the water should be at least warm. For propane, make sure you have propane and the tank is on. Then turn the inside switch on. If you go outside you should hear it fire up and feel the heat by the vent.
You can run electric and propane together for faster heating but make sure both are working.