Dunc, glad you asked about this before it was too late for you. You have heard the right words. You are right, unfortunately the articles tutorials are not very much newbie friendly. Frist let me try to clear some terminology for you.
The thing you need to manage your code and keep track of all the changes you make to your plugins is basically called source code management. There are many opensource and powerful source code manage systems available. Some very famous of them are: Git (not github), Subversion, Mercurial, Bzr.
All of the above SCM (source code management) create a repository for your code and store each and every change you make to your code in that repository. You can move back to any point in history of your code when ever you like.
Github is just a hosting service for your git repositories. Github offers free accounts but will make your code public, a good service to host your opensource applications/plugins.
But if you don’t want to pay and want to keep your code private, then I will recommend bitbucket.org. They offer private repositories and support both mercurial and git.
The first thing you have to do is make the choice and choose a scm. Git is very famous because of its features and Github, but I personally like both, Git and mercurial as they both have very neat features. You can also choose subversion but then you will have to host your repo on your own server or may be find some free service to host your svn repository.
P.S You can also host your git and mercurial repos on your server.