If you are not familiar with CVS, check out our getting started article.
These examples are based on Linux. Let's say your CVS home directory is /var/cvs. Move into your CVS home directory.
~]# cd /var/cvs
You'll need the old version and new version of the file, which you can get by checking the file log.
The cvs diff command can be used to spot differences between revisions.
cvs diff -r <old_version> -r <new_version> example.txt