Git is a distributed Version Control System. Github, on the other hand, is a hosting service for git repositories. I found this particularly helpful: git is the tool for managing source code changes and histories, with github being the service/host for projects that use git.
Also, Github supports git features but also adds its own. An example of its support: the line "git blame" is replicated by the "Blame view" feature in github.
An added feature however will be its project management tools e.g. Github issues.
And, Git is command line based, while Github is a Web-based graphical interface.