Since you are new to all of this, forgive me if I over simplify the water heater issue. Everyone responding to you about the water heater refers to dewinterizing and bypass valves etc. assuming you are familiar with the terms.
It sounds like your dealer did not go over the use of your water heater other than here is where you turn it on. I will make the assumption that you received a generic Thor manual with your motorhome. Go to the section about winterizing your water heater. There you will find a very simple diagram of how the valves should be set for normal operation of your water heater. These valves are located on the back of your water heater. To access them, you will need to remove a panel from the inside of your coach. That panel will be located directly behind your water heater. Set the valves in the position for normal operation.
Now, if you have at any time turned on your water heater using electric, and no water was in the water heater, you burned up the heating element and the element will need to be replaced. My guess is that you did. So, try it on gas and see if you then have hot water. You can continue to use it on gas until you get a replacement element. Depending on how mechanically and electrically inclined, you can replace it yourself.
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