Likely the problem is that you created category groups, but no categories to go inside of those groups. In the categories section of the app admin, there is a tab next to the "Category Groups" header that just says "Categories". It is where you create categories inside your existing category groups, and once that's done, you'll see checkboxes during product creation to allow selection of those categories. Also, when creating categories, you can choose to override the global commission rate for certain categories. Visit Create Category Groups in Marketplace for detailed instructions.