First make sure the water heater is full. If there is still air in it you'll get a lot of sputtering when you open the hot water valve on the kitchen sink.
There are 2 modes for the WH, propane and electric. You can use either one separately or together. LP warms (or re-warms) the water faster, but if you use both together that is the fastest. Turn on the LP mode with a switch inside - a red light next to the switch will light up until it has lit. Turn on the electric mode with a black switch at the lower-left on the water heater - outside - after you open the outer cover. It is easiest to leave that switch on and turn it on/off using the circuit breaker on the converter inside the pod.
If the tank is empty you will burn out the electric element immediately which is why it is important to make sure it is full. Fill it at the start of the season and just leave it full all summer.