Version Management with CVS by Per Cederqvist et al. is the "official" manual for CVS. It can be viewed as HTML or downloaded as HTML, PDF, or PostScript from http://www.cvshome.org/docs/manual/.
Chapter 6 of The LINUX Development Platform: Configuring, Using and Maintaining a Complete Programming Environment by Rafeeq Rehman and Christopher Paul (ISBN 0130826758, Prentice Hall PTR) gives a good introduction to CVS. They give more information, too, on jCVS as well as on how to integrate CVS into Emacs.