Nested folders are folders within parent folders. They are useful when an additional layer of organization is needed to organize your email messages.
To expand a nested folder, simply click on the + icon to the left of the parent folder.
To collapse a nested folder into the parent folder, simply click on the - icon to the left of the parent folder.
Note: You have to click on the +/- icons for each parent folder to expand or collapse them. One click will not affect every folder.