Recents files shows you the latest 50 files that have viewed or edited.
Open files item shows the files from the repository that the user has currently opened in his computer.
Bookmarks shows all the files and folders that you have marked as bookmarks (star icon) in any repository.
The Bookmarks section is intended to provide a quick access to the files and folders that you access most frequently. To add a bookmark to a file or folder, simply click on the star button on the details pane.