Welcome to the forum. Start by ensuring that all your LP appliances are off. Assuming your LP tank has propane, slowly open the LP tank's valve until it's fully opened. Turn one of your stove top burners on and try to light it. It may take a few minutes to get LP gas through the lines if the system has been emptied, so be patient. Once it has lit, let it run for a few moments to purge any air that might be in the lines, then turn it off.
Turn your fridge on, set it to LP and give it a few moments to light. You'll probably hear a clicking sound as it tries to light. It'll give you an error message if it doesn't light off. Make sure your fresh water tank has water in it, then run the hot and cold spigots for just a minute. Turn them off and turn on the LP water heater switch (Usually has a red light when it's on.) Once again, you should hear a clicking sound as it tries to light. You'll be able to hear it when it lights off and is running.
That process always worked well for me. Don't forget to turn the appliances off if you're not going to use them. Good luck.
Kev