Git is a version control system that tracks changes to files. It maintains a graph of commits where each commit is a node. The key concepts covered are Git references, the file status lifecycle between the working directory, staging area and Git directory, and common commands like add, commit, log and status. Branching allows independent lines of development and fast-forward merging can linearly integrate feature branches. Tags mark important points in history. The --amend flag replaces the most recent commit. Remote branches exist on remote servers while local branches are only visible locally.