The git docs are fairly good and github is reasonably (though not excessively) intuitive.
The real appeal, I think - aside from the fact that it's Linus Torvalds clearinghouse is that it allows people to set up what amounts to a mini-wiki/blog. Or actually several of them, since the github is designed to allow you to host many individual projects under a single account ID.
Git's strongest feature lies in the fact that you can work on projects using a local git repo, then push them through to the github repo when you're ready for the world to admire your work.
But that's only part of the deal. The github server understands markdown language, which, like the Wiki markup language allows people to create formatted, hyperlinked documents without the tedium of coding html. So it's typical that a project will include a "README.md" page that show when someone visits your public git repo for a project that can be used to describe the project and how to use it. For example:
https://github.com/mtsinc1/dibs
Among the popular resources hosted at github you can find Docker container definitions and deployment instructions, Puppet modules (and, again, instructions), and so forth. And, of course, this:
https://github.com/torvalds/linux
Some people, when well-known sources tell them that fire will burn them, don't put their hands in the fire.
Some people, being skeptical, will put their hands in the fire, get burned, and learn not to put their hands in the fire.
And some people, believing that they know better than well-known sources, will claim it's a lie, put their hands in the fire, and continue to scream it's a lie even as their hands burn down to charred stumps.
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