The Scan For Media function is available under Import interface for importing media files.
When you select Scan For Media in the Import From panel, a hierarchical folder view is displayed, much like the one shown for My computer. Expanding and collapsing folders works as usual, including the use of the Plus and Minus keys as shortcuts.
Since you are selecting folders rather than files to be scanned, the media files contained in the folders are not shown. A checkbox appears next to each name in the folder tree, and three pop-up lists are offered on the toolbar at bottom. These lists offer a menu of file types to import in each category: Video, Photo and Audio.) By default, the file extensions on each menu are all checked, meaning that all the appearing file types will be included in the import operation. Uncheck the file extensions for any types that you do not wish to import.
To start importing, mark all the folders from which you want to import media files.
When selections have been made, click the Scan and Import button at the bottom to begin the Import operation. This will import all files of the selected types in the chosen directories.