After download, you need to upload this plugin via FTP.
Then you can install it manually via Menu Manager or via the shortcut in the Theme manager.
You should install this plugin before theme installation (because the theme is packed with default data for this plugin), but it's not problem anymore. With our themes there is an option to import demo content after installation directly in Theme manager or you can import just data for this plugin via Database/Tools. In this case, look for XML file inside install folder like install_layouts.xml or demo_layouts.xml.