Git is a source control management tool that tracks files by recording who made modifications, which files changed and what the changes were, and which files were added or deleted. It provides a commit history that allows users to check modifications by commit ID and see what changes were made in each commit. GitHub, GitLab, and Bitbucket are popular hosted Git services that allow users to create remote repositories, initialize local repositories connected to the remote, give access to multiple contributors, and push and pull changes between local and remote repositories.