First you need to create an extension folder. Open your extensions folder.
- Mac OS X:
~/Library/Application Support/StarUML/extensions/user
- Windows:
C:\Users\<user>\AppData\Roaming\StarUML\extensions\user
- Linux:
~/.config/StarUML/extensions/user
git clone git@github.com:Obversity/StarUML2-Rails-Generators.git rails_generators
Tools -> Rails -> Generate Generators
Select the diagram with the models in it, plug in the generator type you want (i.e. model, or scaffold, or any custom generator) and grab your generator commands.