The categories are the styles in which the AutoText entry is formatted when
it is saved. See http://word.mvps.org/faqs/customization/autotextcontent.htm 
and http://www.mvps.org/word/FAQs/TblsFldsFms/AutoTextList.htm.

Ricki,

To add an AutoText Category you only need to create an AutoText entry in a
style with a like name as your category.  To delete the category, delete all
AutoText entries defined for that style.

Lets say you want to create a new AUTOTEXT entry in the Salutation category.
Apply the salutation style.  Type in the new salutaion -

Dear Bozo the Clown

Select the text and press ALT+F3 and name the entry

If you look at the drop down menu the new entry will be included.

HTH

See:
http://word.mvps.org/faqs/customization/AutoText.htm