When Folder Sharing is Enabled (see also: Enabling Report and Dashboard Folder Sharing) your Users will have the option to Share Report and Dashboard Folders with Public Groups or select Users. There are three levels of access for Folder Sharing. Viewer, Editor or Manager. This Article discusses the differences between those access level options.
To Share a Report or Dashboard folder, go to the Reports Tab. In the Report Folder list along the left-hand side of the screen, hover over the Folder you'd like to Share. Click the Pin icon, then click Share.