Wolfman and Dracula have been hired by Universal Missions (a space services spinoff from Euphoric State University) to investigate if it is possible to send their next planetary lander to Mars. They want to be able to work on the plans at the same time, but they have run into problems doing this in the past. If they take turns, each one will spend a lot of time waiting for the other to finish, but if they work on their own copies and email changes back and forth things will be lost, overwritten, or duplicated.
The right solution is to use version control to manage their work. Version control is better than mailing files back and forth because:
On Wikipedia all changes and their authors are tracked. You can go here and you will find the history of all changes done to the article about the planet Mars. Find the last edit done last month and look at the changes made by clicking on the "prev" link on the left of the history entry.
This lesson shows how to use a popular open source version control system called Git. It is more complex than some alternatives, but it is widely used, both because it's easy to set up and because of a hosting site called GitHub. No matter which version control system you use, the most important thing to learn is not the details of their more obscure commands, but the workflow that they encourage.