Create an account in the Web site and add yourself to the EditorGroup. This will allow you to create and edit pages for adding documentation or translations, for example.
Create an account in Savannah. Savannah is the project management system used by gNewSense contributors. There you will be able to get access to gNewSense source code, and use the task and bug trackers if necessary.
Get familiar with the gNewSense Processes that interests you most.
All the communications between gNewSense contributors take place in the
development mailing list and IRC.