Here are slides containing more content than a blackboard talk I gave in May 2015 in Freiburg:
Git versioning (why and how) for Mathematicians
Git Logo by Jason Long is licensed under the Creative Commons Attribution 3.0 Unported License.
Git for Mathematics
Why mathematicians should use (distributed) version control systems like git, and a small tutorial to get you started.
Comments
As a minor update I want to remark that I have successfully convinced one person to collaborate using Git although he did not use Git before, and I have got very positive feedback from my fellow PhD students who tried Git.