With eCart you will have your items information come directly from your database, there is no special importing or anything like that. You can just create a page to display some items based on category or however you organize them. On this page you would just have a recordset that selects the records from your db. This will let you have a page listing items from your db and you can add in the add to cart functionality so these items can be added to the cart for purchase.
The best place to get started on this is the eCart support page here: