You can do this locally as everyone mentioned using
git checkout -b <branch-name> <sha1-of-commit>
Alternatively, you can do this in github itself, follow the steps:
1- In the repository, click on the Commits
.
2- on the commit you want to branch from, click on <>
to browse the repository at this point in the history.
3- Click on the tree: xxxxxx
in the upper left. Just type in a new branch name there click Create branch xxx
as shown below.
Now you can fetch the changes from that branch locally and continue from there.