If you haven’t heard of the term Git (Git Version Control System), you can skip the story and google the term to know more about it.
And if you are aware of it and looking for a handy document, where you could refer all the commands in a single glance and learn more, checkout the website by Roger Dudler, which explores all the important Git commands in a very simple, plain English and in an appealing way.
The website: http://rogerdudler.github.io/git-guide/
And if you wish to download the same in PDF format, you can download it from the same website as well or from the below shared link.
Download: Git CheatSheet PDF