This is a brief intro summarizing my experience using Git/GitHub. You can find configuration information and some very basic commands here. For more information, Google and Stack Overflow will always be your best friend.
They are different things. Git is a software that does version control, while GitHub is a platform that help manage Git repositories (repos afterwards). You do not have to use GitHub to access Git, as you do not have to use RStudio to use R. But GitHub helps you better manage Git repos, store files on cloud, collaborate with others. Therefore, this intro focuses on how to use Git and how to communicate with GitHub.
Reminder: do not put your Git repos under Box or Dropbox folder in case of synchronization issue.