Welcome, the folks here are great. As you probably noticed, the user manuals are too generic as to be useful. I tried to fire mine up a few weeks ago, and actually had to call Suburban (the maker of my furnace). I believe that all you need to do is ensure that you have propane coming through your lines (check stove top first and clear air if necessary) and then slide the thermostat up all the way. It may take 30 seconds or so to fire up. While the furnace has an on/off switch, that should have been set to "on" by the dealer who sold the unit to the original owner. You can't actually see the switch on mine, so it must be under the housing, and inaccessible to me. Troubleshooting involves making sure that the wires in the thermostat make contact, and/or that the propane line to the furnace is not damaged--plenty of info online.
2007 X160; Nissan Frontier 2016 6cyl