Each product is displayed on a generated product page. You can add other elements onto this page to create a long description for your product. To do this, in the editor, click on the product as it appears on a category page, in a product element, or from the Edit Product page. This brings up the product page in the editor and you can change it as needed.
Note: To see the Go to product page link on the Edit Product page, you first need to save a product, then go back and edit it.
At the bottom of the product page you'll see an area for the long description, which will be empty if you have yet to edit it. You can drag elements from the Build tab into this area just as you can on any page, and it's a good way to include additional information on a product without cluttering up the short description area.
The long description can also be used creatively in many ways. For example, you can drag a Products element to the long description and suggest an item that is similar to the one being viewed. Try it out in your store and see what you can come up with!