The tutorials installed with Dark GDK are here: Start menu, Programs, The Game Creators, Dark GDK folder. There you have access to documentation, samples and tutorials. These can also be found in the file structure, in default installation it is c:\Program Files\The Game Creators\Dark GDK\ and then the same subdirectories: documentation (the help, which is a list of available commands), tutorials or samples.
The Dark Invaders tutorial is available in video format as well:
http://forum.thegamecreators.com/?m=forum_view&t=139595&b=22
Daniel started a video serial which does not have much info yet for Dark GDK, but for example, I liked the frogger game tutorial for DB Pro and it would be quite a nice starting challenge to try to do something similar in Dark GDK. I think he will make the corresponding video sooner or later, in the meantime you can try for yourself.
http://forum.thegamecreators.com/?m=forum_view&t=163667&b=22
It is true that more tutorials can be found for DB Pro than Dark GDK but nevertheless, you can get started.