Folders provide a way to organize email messages, calendars, contacts, and tasks in Outlook.
Important: Steps may be different between the new and classic Outlook for Windows. To determine which version of Outlook you're using, check if there's a File option in the menu (located above the ribbon). If there's no File option, follow the steps under the New Outlook tab. If File appears in the menu, select the tab for Classic Outlook.
In the folder pane on the left, right-click the folder that you want to add a subfolder to.
Select Create new subfolder.
Enter a name for the new folder, then press Enter.
To add a folder to the folder pane, do the following:
In the left pane of Mail, Contacts, Tasks, or Calendar, right-click where you want to add the folder, and then click New Folder.
Note: When in Calendar, the New Folder command is replaced with New Calendar.
In the Name box, enter a name for the folder, and press Enter.