You must set up at least one category before you start using Fastpage.
It is important to understand the structure of categories as apart from being able to structure your Fastpage web site, users can be restricted to one or more categories.
This means you can assign users to work on certain parts of the web site but not others.

The title is used on most Drop down displays when you select a category to attach a template or Menu to.
You can re-assign categories attached to a template or menu at any time.

The Description is just free text you can use or elect to leave blank - it is not used anywhere else except on managing or adding new categories.

Summary:-

• Users can be restricted to one or more categories
• Categories help you structure a Fastpage site
• You can reassign categories attached to templates and menu's at any time
• You can not delete a category where there are menu or templates attached
• Number of categories is unlimted only restricted by SQL restrictions or disk space
  (generally more than enough - were are talking 1,000's of categories)