In previous versions of Outlook, your folders were sorted alphabetically. What annoyed me is that they were sorted among the Drafts folder, Sent items, etc. To work around this, I either put all folders under my Inbox or in a special folder I labeled "My Folders."
With Outlook 2013, you can move your folders anywhere you want by clicking and dragging. You'll notice when you move a folder, a gray highlight bar appears to let you know where it is going. Watch the dark gray horizontal line to determine it will drop into another folder, be a main or a subfolder.