You can put any file under version control by simply visiting it, and
then typing C-x v i (vc-register). After C-x v i,
the file is unlocked and read-only. Type C-x C-q if you wish to
start editing it.
When you register the file, Emacs must choose which version control
system to use for it. You can specify your choice explicitly by setting
vc-default-back-end to RCS, CVS or SCCS.
Otherwise, if there is a subdirectory named `RCS', `SCCS', or
`CVS', Emacs uses the corresponding version control system. In the
absence of any specification, the default choice is RCS if RCS is
installed, otherwise SCCS.
After registering a file with CVS, you must subsequently commit the initial version by typing C-x C-q. See section Using VC with CVS.
The initial version number for a newly registered file is 1.1, by default. To specify a different number, give C-x v i a numeric argument; then it reads the initial version number using the minibuffer.
If vc-initial-comment is non-nil, C-x v i reads
an initial comment (much like a log entry) to describe the purpose of
this source file.