GitHub is a website and service for storing and building software. You can work on GitHub using its graphical user interface or using command-line utilities. On the other hand, git(1) is a command-line utility that can do many things, including working with GitHub repositories.
An alternative to GitHub is GitLab. Most, if not all, of the presented git(1) commands and options will work for communicating with GitLab without any modifications.
This section will offer you a quick introduction to git(1) and its most common and frequently used commands.