Office 365 (Outlook Client for Mac) - Add or Remove Folders
In Outlook, you can create folders to better organize your messages.
This Microsoft help article explains how to both add and remove folders: https://support.office.com/en-us/article/add-or-remove-a-folder-in-outlook-for-mac-71948772-18f5-4ef6-b8a4-396e70d70598