Categories in SimpleCart are custom resources. This means they provide additional features in the manager for listing products and setting a couple of options.
Add a new category to your shop
Use the right mouse click context menu in the resource tree to use the "Quick Create" feature of MODX. Fill in the basic details, and when saved you can see the category interface in action.
You can also create categories by using the regular Create option. This will open the Category interface for the new resource directly.
Last but not least, you can use the toolbar "shopping cart" icon to add a new category. You should keep in mind that a category created in this way will be located in the root of the site.
Modify the category
Next step is to configure, setup and fill the category.
There are several things you can do with a category, including managing products.
The basic fields at the top are similar to the standard resource fields. Below these fields you can find the products (if any) in this category (4).
You can also set a default product template on the right-hand site of the screen (3).
But hey? Where's the content?
The content area has been moved to a Content tab (1). This gives you more room for the product listing.