With an urgent fix to make, you create a branch for it, cal it hotfix, where you do your work until it's competed:

$ git checkout -b hotfix

$ vim followers.html.erb

$ git commit -am 'add followers feed'

[hotfix 3a0874c] add follower feed

1 file changed, 13 additions(+)

hotfix branch based back at the master branch point

At this point (HEAD points to hotfix), you can run your tests (more on tests here: http://agiledata.org/essays/tdd.html), make sure the hotfix produces the desired output, and merge it back to the master branch and deploy it to production. Merging is achieved with the git merge command:

$ git checkout master

$ git merge hotfix

Updating f42c576..3a0874c

Fast-forward

Your change is now in the commit pointed to by the master branch and is ready for deployment.