How do I create a subcategory?

All categories on our system are created in the same way (through the add category page).

The difference between categories and subcategories is explained in this article. Briefly, what makes a category a subcategory is that it has a parent category assigned to it.

To assign a category a parent category when adding/editing the category scroll to the 'parent categories' section and select the category's parent category from the drop down list.

You can assign up to 3 parent categories to a category by default, so to choose another select + add another and another drop down list will appear.