From the Categories (Admin Control Panel -> Tables) menu, users can add classes (elements) of objects relevant to their sites.
Table (header, principal) elements contain tables with subcategories for search purposes. To add new subcategories click on the button on the left side of the desired category.
Example
The Antiques category has been populated with several subcategories related to it.
Alternatively, on the right side of a major category, there's the Edit Options button.
From the menu add/edit the following options: