What could cause a mobile home furnace not to light?
Does the pilot light and stay lit when you hold in the control knob in the "pilot" position?

If yes, you may need a new thermocouple, it is the little tube looking thing next to the pilot flame area. When it gets heated it sends an electrical signal to the gas valve which allows the gas to flow and the pilot to stay lit (and burner to light). 

If no, you have a different problem. Check to ensure the gas supply is not obstructed or turned off; make sure you are closely following the lighting instructions. You may need a new gas control valve. Call your gas supply utility, tell them you need help and they will send someone out (usually for free) who will be able to diagnose simple problems and sometimes fix them. You may have to call an HVAC professional if nothing else works.