The CS-RCS Repository keeps track of your various file revisions. Each file you want to keep track of must be added to the Repository. Whenever a file receives a significant revision, add it again to the Repository so that you can return to that revision at a later stage if needed. Adding a file to the Repository is called checking-in a file.
You can always retrieve any revision of a file from the repository at any time. This is useful if you wish to undo your changes. Retrieving the latest revision from the Repository is called checking-out a file.