If you clicked on the Products tab, you may have noticed the Categorize button as well as the "Category" column and filter. These refer to reporting categories which are used primarily to organize your products and improve the quality of your reports. They are optional for all products.
To add or edit your reporting categories, make sure you're on the Products tab, and then click on the Reporting Categories section of the sidebar menu. From there, you can click the Add Product Category button, or edit or delete an existing category.
When you're satisfied with your reporting categories, you can assign them to one or more of your product records by clicking the on the Products section in the sidebar, checking one or more boxes to select product record(s), clicking the Categorize button, and choosing the desired reporting category.