GitHub is a version control tool and social network for developers that allows them to share code, build portfolios, and save projects. It uses Git in the background for collaboration, storing changes, reverting to older versions, and reviewing code changes. Users create a GitHub account to access repositories, which are storage spaces for projects that can be public or private. The document then demonstrates how to create a repository, commit and push code changes, resolve conflicts, and write a README file using Markdown formatting to provide information about the project.