Unfortunately, GAJET is not very well documented yet. For new users it is hard to start using it. I recommend all new users to perform the following actions to became more familiar with GAJET:
1. Download GAJET
2. Define JAVA_HOME environment variable. It should contain path to installed JRE.
3. Run gajet and modified EMMA. Use bin/gajet.bat and bin/gajet-emma.bat files on Windows, bin/gajet and bin/gajet-emma scripts on UNIX-like systems. On successful run they should display brief usage information.
4. Proceed with step by step example (Example.html file from GAJET distribution).
5. Try to use GAJET on your own simple classes.
6. Look more complicated examples in SVN repository (http://gajet.svn.sourceforge.net/viewvc/gajet/gajet/trunk/gajet-tests/).
7. Ask your questions in this forum.