UI.X2 Column sub-forums

I understand from the title and content what this is for, but I also have a lot of experience, where as not everyone has it. It would probably be a good idea to elaborate on this a little bit.

What is this for?
What content does this change, and specifically how does it change it?
How do you navigate to the changes?

Just remember that no everyone has the same knowledge as you. Express yours by simplifying everything for those who don't!