RCS Basics ( Building a Simple Local RCS Repository)

Create a subdirectory named RCS in your private working directory:

$ mkdir RCS

Check in files you want to add to the repository (this moves them into the RCS repository):

$ ci foo.c
$ ci blah.c

Check out file you want to work on (-l locks the file so only you can check it out to modify it):

$ co -l foo.c
$ co -l blah.c

Subsequent check-ins create a new version of the file, and you can revert to older versions by using the -r flag with co (see the man pages for co and ci for more details).
Some other commands (and see man page for rcsintro):

$ rcsdiff foo.c    ( diff between foo.c and latest version in repository)
$ rlog  foo.c      ( see the log messages associated with commits to foo.c)