The Link Files and Link Folders options within OverDRIVE allow you to quickly add files or folders from anywhere in Google Drive to your active OverDRIVE folder (ie the current page you are on). If the page you are on is a Folder Page Type you can click on the + icon to open the Add Content options. Choose Link Files or Link Folders within the dropdown. Choose the files or folders  you wish to add and click the Select button. If the page you are on is any other Page Type you can only link folders. Open the Site Menu and choose Link Folders.

Note: you can only Link files or folders on certain page types (eg Folder View); where you can’t add a file or folder, the option will be hidden on the menu.