Hi Lilly,
Welcome to Auctiva!
You can NOT sell on ebay until you register as a seller. It is a simple process consisting of updating your existing ebay account with credit/debit card or checking account info. This information is required so that ebay knows how you will pay the fees for your listings. Use the following link. It explains the basic info and at the bottom of section 2 gives you the link to "become a seller".
Creating a Seller's Account
Once you update your account you are ready to start creating and scheduling/posting your listings on ebay through Auctiva.
Hope this helps and Good Luck Selling!
Terence
COZI COLLECTIBLES