Actually the Perfect world is the category, while Class Discussion is a forum and (forums) are the sub forums...
When you create a sub-forum you need to answer the
List subforum in parent-forum’s legend: Yes, that will display the sub forums on the main index as it does on my
test board (in the "Welcome forum" section).
To put your already created sub-forums on the index just go to the
ACP ->
Forums ->
Manage forums -> click on the Edit image
by the sub forum -> mark
Yes by the "
List subforum in parent-forum’s legend: " question and click on
Submit.