Most product catalogs are separated into categories and subcategories and maybe even sub-subcategories. Products are then assigned to appropriate categories in order to help visitors find the kinds of products they're looking for. There is no limit to the number of categories you can have, and there's techniclly no limit the number of levels of categories that you can have, though we recommend no more than three levels for ease of use. Products can also be assigned to multiple categories.
Imagine that you have a website that sells cars. One category might be "make" where you can choose from Ford, Chevy or Toyota, or any number of other subcategories of vehicle manufacturers. Another category might be "size" and have subcategories like Compact, Sedan or SUV.
To communicate this to us, simply type it out in a bulleted list, like: