This is the left, smaller side of the library area which contains different options and settings.
The different options and settings contained in this section includes the following:
New Folder: Clicking this will allow you to create a new folder that gets added to the Library.
Rename: This will allow you to define a new name/change the name of a selected folder in the Library.
Delete: This option will allow you to delete a selected folder from the Library (you should use this function with care as the action is not reversible, though, all the existing files from the deleted folder will be automatically associated to the uncategorized folder).
Sorting Icon: This option allows you to sort folders and files by ascending or descending orders of their alphabets, name, date e.t.c.
Hamburger icon: This icon shows the folders bulk selection option.
Divider Icon: This allows you to change the size of the media gallery sections to suite sight.
All Files: This is an automatically generated/created folder which keeps/contains all the media files you have uploaded on your website. This folder is not modifiable, so you cannot delete or rename it, you can only work modify the files in it.
Uncategorized: This is the second automatically generated folder which is shows only the media files that doesn't belong to any categories yet. Like the "All Files", it is also not modifiable, so you cannot delete or rename it, you can only work modify the files in it.