To use categories you must follow this procedure in the order given:
1. Go to forum settings, click on the categories link.
2. Enter the categories you want to use, make sure you enclose the category names in brackets, e.g. [Category 1][Category 2] and so on, then click submit.
3. Go back to the forum settings summary page. On each forum line there is a dropdown box for category, select a category for all your forums. If you do not assign a category to a forum it will not display in the forum summary.
4. Now go to your general settings and look for the display categories option and turn it on.
That's it.
As to your second question, there is NO METHOD to delete forums in UBB5 versions. This however is a feature of UBB6 if you wish to upgrade.
You can however get a deleted forum effect by first turning off the forum, pruning all the posts, and if desired make it private.
