How does it work? Can we go even if we are staying at OKW?
Yes, it is open to everyone; you don't even have to be staying on Disney property
Does it cost anything or is it outside?
It is free of charge. It is outside with bleacher seating. There is an area to bring your own chairs if you wish.
Can we bring snacks?
Yes, you can. They do have a chuckwagon that sells sncacks including smores "kits" for the campfire.