As stated in the introduction, 6wall was derived from Shorewall. If there are any unclarities about how to configure a specific file or option for 6wall, a good starting point is to check out the documentation of Shorewall for your issue. The Shorewall documentation is very exhaustive and there is a good chance that you'll find what you're looking for.

Remeber, the documentation here mainly focusses on the differences between Shorewall and 6wall. The section Reference goes into the 6wall specifics of the available configuration files.