Hi,
What have you tried so far, and what specifically happened?
In the absence of other information, the basic workflow from getting an `.ass` file out of Gaffer is to use the Render node in SceneDescription mode, as in the screenshot below :
Render nodes are task nodes which can be dispatched as part of a farm job, but here I'm just using a LocalDispatcher to run it on the local machine. When you press the "Dispatch" button, the work should be done, with feedback on the job shown in the Local Jobs panel.
Cheers...
John