Categories
Creating categories and assigning products.
Categories organise the catalogue: a business-wide tree, one level of parent per category, and any number of categories per product — a Ceylon tea can sit in both Tea and Gift ideas.
Who can do this: full category control belongs to the Admin and Inventory Manager roles; assigning products to a category is its own permission, so a custom role can curate the tree without being able to rename it.

Add category asks for a name (unique among your categories), an optional parent — "None (root level)" makes it a top-level group — and an optional description. Each row's menu can also add a sub-category directly beneath it.
Products join a category from either side: from the category's Manage products action, or from the product's own form. Large assignments are saved in batches — adding a whole range to a new category works, it just takes a moment.
Deleting is deliberately gentle, and the dialog spells it out: "Its sub-categories are kept and move up to this category's parent. Products lose only this category. They are not deleted."
So removing a middle layer of the tree flattens it rather than orphaning anything: children step up to their grandparent (or become top-level), and every product simply loses that one chip.