Office 365 (Outlook 2013 / 2016 /2019 for Win) - How to View Subfolders Within a Folder

If you are having trouble finding your folders in Outlook, here is a tip to help you expand your folders to find the sub-folder/s within. 

Click the hollow triangle to the left of the folder to expand it and the sub-folders will appear.  When the triangle is solid black, it means that the folder has been expanded.