Git and similar tools are designed to track multiple revisions of a file. Imagine the history feature (undo/redo) from your favorite editor, but for saved files, and with the ability to point to two arbitrary versions and ask, "What changed between these?"

On top of this, Git added the ability to merge changes together automatically. Imagine that one person changed a bunch of stuff in the first paragraph in a document, and someone else changed a bunch of stuff in the second paragraph, and the computer could automatically merge those changes into one document.