You need to do this only once. The instructions here are very similar to the instructions at https://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 matplotlib 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.
Log into your github account.
Go to the matplotlib github home at matplotlib github.
Click on the fork button:
Now, after a short pause you should find yourself at the home page for your own forked copy of matplotlib.