You still need C++ code to deal with User Interface changes triggered by user actions, but using libglademm for the basic widget layout allows you to focus on implementing that functionality.
Gnome::Glade::Xml must be used via a Glib::RefPtr. Like all such classes, you need to use create() method to instantiate it.
Glib::RefPtr<Gnome::Glade::Xml> refXml = Gnome::Glade::Xml::create("basic.glade");
This will instantiate the windows defined in the .glade file, though they will not be shown immediately unless you have specified that via the Properties window in Glade.