mdash is an extension that creates an empty browser tab filled with your bookmarked sites. If you wish to create a dashboard with mdash, you first need to create a special folder named [Dashboard] in the Other Bookmarks folder of the bookmarks application.

Then you can open the Bookmarks Manager and browse to the folder and add the new section with a name and open the window.

If you want to add an element to the section, you need to select it from the list of folders that are created by the extension. In case it is not added to a section, it will appear on the left column of the browser.