All 3 are mains switches, nothing to do with your 12 v circuitry, it's your fuse box from the power inlet, just like in your house.
The 2 switches on the left are your circuit breakers for seperate circuits for fridge (I would think) & sockets whilst on hook up, the one on the right is the main breaker / RCD, it overrides the 2 and the button at the top is to test the trip out,... Switch all 3 on, press the button & it should switch off again. Not very well explained I know, but hope it gives you an idea of what it should do.
Gas can & often does take a long time to get to a fridge, or the igniter / burner / thermocouple might be poorly, do a search for fridge problems, there's lots of info. Is the fridge's gas supply definately on, leaking hose to fridge? It will (probably) be a seperate tap to the cooker supply.
What conversion is it? Someone may be able to point you to the correct manual for all the different bits, or get Googling
You'll probably get better info after the weekend when all the lucky people are back from Oswestry
If you're unsure about anything Gas or electric related, please have it checked over by someone who really understands what they're doing, if there are no members nearby who can help you out try a local caravan service centre. Flexible gas hose has a limited usable life, there should be a date on it, and it's not expensive to replace, (again caravan dealers)
Hope this helps a bit
Andi