The very first step before going deeper into ATOM3's graph grammar is to verify that your setup is up to date. First, get the latest version of ATOM3 there. Also, ensure that your version of python is at least 2.2 for the graph grammar algorithm to work correctly. Type python, python2 or python2.2 on the command line and press enter to check your version:  

Then, type Ctrl-Z to exit the python shell and go into ATOM3's directory. Take notice that ATOM3 runs on any machine having python 2.2 installed. Type this to load ATOM3 (or python2, python2.2 depending on your setting):  

You will see two main windows in ATOM3 graphical user interface. One is called "console" (fig 1) and is used to output information related to ATOM3 operations (Ex: code generation). The other one (fig 2) is the main "canvas" used to design models, meta-models, graph-grammars, etc.  

Fig. 1  

Fig. 2

The first thing to check is that the options of ATOM3 are set correctly. Click on "file", then select "options". Be certain that you have created a personnal directory for your work and that you have added it to the "code generation" section and the "Path directories" section. In our case, the directory we use is called "Sumproj" :