You don't say what model fridge you have; but basically you push the button in, the Auto light illuminates, and it goes to electric if it has it. If it doesn't, it switches to gas. If you push the button again (so it comes out), then it will just run on gas. If you don't have gas available, it won't run.
When it does try to run on gas, it will attempt 3 lighting sequences. If the gas hasn't lit off in those 3 trys, it will lock out.
Maybe the attached docs will help. If you're still having issues, post your model number and more detail on your problem and someone will probably try to help you.
1988 Coleman Sequoia - popup (1987-2009)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10