Where there isn't official documentation available there is The UBB.Wiki Project available that has contributions from various users here at UBB.Central.

The UBB.Wiki Project is a documentation set compiled by users of UBB.threads. The UBB.Wiki Project was created by Gizmo and Ruben during the summer of 2011 with the goal of documenting as much of the UBB.threads forum software as possible (as well as providing numerous guides and articles).

If you're interested in helping contribute, please see here. If you'd like to have a topic covered, please send a Private Message to both Gizmo and Ruben with your requests.

Considering the large scale of current (and upcoming) features we tend to just hit sections "when we get to them", so by alerting us as to what you'd like to see specifically allows us to target a specific topic.