I have been using TFS in my previous workplace and my new workplace uses GitHub. So this is how i got started with GitHub.
I first started with the following links to get introduced to git (which intorduces github to even non developers)
Then, I was told my company uses a gui instead of the git command line, tower.
So here is how I got started with tower
Also, this could be of help
Find an online ebook here
I am still not done with these videos. Will update once done.