On reaching the Documents screen of a collection, user can view the folder structure (in tree format) within the collection on the right-side of the screen.
On the left-hand panel user can refresh the folder tree (which will enable any changes made to the folders like folder addition, folder removal, folder rename etc. made on the same account and in the same collection but from device by the same user or from web another user, to be reflected here), create new folder and move folders up & down to change the sorting order. Also, user can click the [More options] button to perform various operations on the folders.
User can click the [Plus] sign beside each folder to view and access the nested folder under that folder. This sign also means that there are nested folder under that folder.
Screenshots below displays the 'More options' menu through which user can perform various types of operations on the folders: