I am sure you have a electronic spark ignition on the propane part of your water heater. Just turn the switch on (probably in the bathroom). You will see a short red light flash and then it should just run. The light will go out and only come back on if there is any problem.
I assume you will have the propane tanks on. Light the stove for a minute to be sure you have propane available in the pipes
This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.