Hello misspat,
For your eBay store categories to show on the listing creation page in Auctiva you first need to ensure that your account is current with eBay. For this please select 'eBay' from the My Account menu after logging in to your account and on the ensuing page click on the 'Update eBay Preferences' button, which will update your available store categories.
You can then select from your store categories on the lister page in the store category pull down menus available there.
If you run into difficulty with categories after such an update please feel free to file a support case from under the Help tab of the site letting us know what you have tried and what the results have been and we'll be happy to look into it further.
-Craig