Depending on which version of ShopSite you are using, you can go to Products, Select the products you want to display on eBay and click the Download button. Then on the download screen select the eBay® Turbo Lister file format and download your file. You can then use that to upload to Ebay.
Note that it has been a while since ShopSite implemented the ebay download functionality and it has not been changed since then. If ebay has made changes to what they need you might need to create your own download file format using the "Selected fields only" option on the download and select the fields you will need.