The store module works by grouping products into categories and then mapping categories to Documents, doing this allows the store to support almost any site structure that you may require.
To create a category click Categories on the dashboard and then Add Category, enter the name of the product category in to the field labeled Category Name and click Create Category.
Next you need to make the category visible on the website, to do this first take note of the category number, this is the number in the square brackets:
Next return to the Dashboard and select Documents, at this point either select an existing document to hold the store category or create a new document.
In the Content field place the following in order to display the products from the category:
Next scroll to the bottom of the page and change Document Behavior dropdown to Container for Store Product Category and in the box next to it enter the category ID, in this case 2, then save the Document.
As you add products to the category they will appear on the public interface of the website with the category root being the selected document.