Did you know that when you create a document in Google Drive that all changes are automatically saved? And did you know that after all changes have been saved in Drive that it becomes a hyperlink that will launch the revision history when you click on "All changes saved in Drive"?
After clicking on "All changes saved in Drive", the Revision History will appear on the right side of the screen. The Revision History lets you see who made what changes and when those changes were made. It also allows you to revert back to an older version of the document.