The best place to get started using the TARGET GUI is the Thrustmaster TARGET GUI PDF manual. It is installed along with your software. I think you can access it directly from the GUI or you can find it in the installation folder for the software. The manual is fairly complete, offering both simple examples and advanced examples. It does a good job of explaining all features of the GUI. If you haven't already, you should read through the beginning sections of the manual for an overview.
If you prefer to learn by example (like a video), search for "thrustmaster target gui" on Youtube. There are many videos that explain how to use the TARGET GUI.
The process is the same for all TARGET compatible devices. So if you find a video on, for example, the Warthog Throttle or Stick, the examples given should work exactly the same for the T.16000M Stick and TWCS throttle.
The reason you don't find many forum topics discussing the TARGET GUI is because once you get past the basics, it is very easy to use.