How do I. . .

[Brap]

Make the sub forums show up under a forum?

 

[Dvir130]

HTML or "Arrange Sub-Forums in columns"

 

[Boss_013]

check it in Here
Admincp->Option>Forum Listings Display Options>Depth of Sub-Forums
Set it like 10,50 or more it depends how many sub-forum need to display.
thanks