You need to do this only once. The instructions here are very similar to the instructions at http://help.github.com/forking/ - please see that page for more detail. We’re repeating some of it here just to give the specifics for the dipy_ project, and to suggest some default names.
If you don’t have a github account, go to the github page, and make one.
You then need to configure your account to allow write access - see the Generating SSH keys help on github help.