Once all of your settings have been completed (e.g store settings, product listing template and shipping - the dashboard will prompt you if these are not complete or go to 'Settings - Configuration to check) all you need to do is map your products to eBay categories.
From the dashboard, under the 'Reasons for not being listed' section you will see the total number of products that require mapping. Click through to the Mapping Pages, the process of mapping products also uploads them to eBay.
For more help on how to map, check out the Category Mapping FAQs.