It seems like the ability to add subfolders is basic to organizing emails and it appears that AOL users have been asking for this for years.
Bert & Lori Schoose commented
I can create sub-folders without any issues. On the left side of my screen, there is a button that is below Folders that has "+ New Folder". When I click on that, it will create a new folder for me.
If I want to create a sub-folder below that, I then put my mouse over the newly created folder so it is highlighted and then I right mouse-click on it. At the bottom of the resulting list that pops up there is a "create subfolder" choice. I click that and it creates a sub-folder below what I previously created. I've been able to do this for years.
Note that you can do this with a folder that was created some time ago as well and not just when it is a newly created folder.
I hope this helps with what you seek.
ROB HOFF commented
Boy, do I agree strongly with this one!
I have questioned your technicians about this, and have been told repeatedly that you CAN add sub folders.
Damned if I can find how!