Aha! The instructions say, "From the main menu, select More tools > Bookmark Importer." But the fly in the ointment is that the 'Bookmark Importer' option is grayed-out. So does that mean that there is no way to import bookmarks into Opera??
It should be enabled if you had imported your old Opera Presto profile into your Opera Blink one.
You can't import directly the bookmarks from other browsers. You'll nedd to export them as html, open the file in Opera, access each link and bookmark one by one; or maybe use a extension or 3rd part tool.