Hello Lee,
You should have been given the instruction manual for the appliances when you purchased the caravan, if not check with your seller.
If the fridge does not work on any of the supplies, then that strongly suggests that it has lost all of its refrigerant fluid. Some times the fridge can be recharged, but if not then it is scrap. Speak to your local caravan or air conditioning specialist about getting it checked out.
At that age you almost certainly have a Carver heater. All these heaters work on the same basic principal, as does the gas side of the fridge. The gas valve has to be rotated to the ignition position and pressed in fully, At the same time the piezo spark ignitor should be pressed in several times at about 1 second intervals. Normally the gas will ignite in the pilot setting. Keep holding the gas valve in when the flame has lit for about 15 seconds. This allows the flame to heat up the thermocouple flame failure device, which should then allow you to release the gas valve knob. The flame should stay lit, at which time you can adjust the valve to your desired working setting.
If the fire is not igniting then check for any gas distribution/isolator valves that might have been turned off under the sink or cooker or in lockers etc.
I must remind you that all service, installation or removal of gas appliances, including the breaking & making of gas joints must be performed by a competent person working to the gas regulations. If you are not competent then you must refer this work to a competent person.