First you will need a C# editor (Windows, Other)
Then you will need to download the source
Open up the main project file and run.
<insert screenshots here>
This is an example session of the tutor. To understand a bit more what's going on computationally, take a look here and here
Note that the above papers are about AutoTutor. The GnuTutor deviates from AutoTutor in the ways described here (under preparation).