Subcategories can be used to create a 2nd level in your catalog structure.
A subcategory needs to be assigned to a single category. It can contain as many products as you want.
If you have chosen to use subcategories for your catalog structure in Global settings then Subcategories will appear under Apps / Catalog / E-commerce System. You can add as many subcategories of products as you want. Once a subcategory has been created you can assign products to it.
Assigning a subcategory to a category
Notice that a subcategory needs to belong to one – and onle one – category.