When you are filling out the form that adds a new forum, there is a drop down menu labelled: "Add to which parent?". You should change this box to your "chit chat" area.
E.G.
Code:
Category 1
-Forum A
-Forum B
-Forum C
In order to add subforum to Forum A then you would follow the steps above, substituting Forum A for the forum you wish to add a sub to.
New Layout after addition:
Code:
Category 1
-Forum A
--Subforum I
-Forum B
-Forum C