WP eStore should already be set up on your website with the initial products that you started out with when we initially designed your website.
However as you go along you might find that you need to add new products.
WP eStore has created extensive documentation on their website.
Check out their website WP eStore Documentation Index for loads of information on how to do different tasks.
Most of the information that would be relevant will be under the “Design and Usage” and “Shipping and Tax Related” and “Admin Options”.