Very similar to one I had in my old camper. Dead simple to operate. My old one was very reliable, and much more dependable than any of the fan operated furnaces I have had since.
1 Make sure you have gas getting to it.
2 Open the little round hatch.
3 Turn the gray knob to pilot.
4 Probably have to push the gray knob in to start the gas flow.
5 Once the gas is flowing, listen for a low hiss, light
the pilot flame.
6 Look in the round hatch. You should be able see the flame going up onto the thermocouple probe.
7 Hold the gray knob in until the thermocouple probe heats up. Usually about ten seconds.
Release the gray knob. If the pilot light
goes out repeat the lighting
procedure, and hold a bit longer.
8 once the pilot light
is burning steadily advance the white knob to the desired temperature.
9 The main flame should light up within a couple of seconds.
10 close the little round hatch.
The only problem I had with my old gravity furnace was when the little hood over the pilot light eroded away slightly. I had to reshape it to keep the pilot flame on the thermocouple probe. If the pilot flame does not stay on the probe the furnace will shut down. It is a safety feature.
PS: Some rvs have a seperate shutoff valve in the line going to the furnace. If you do not get gas going to the furnace look for a valve other than the one at the tank.