Make a commit
The message has to come first:
cvs commit -m "Message" /path/to/file
Commit multiple files
cvs commit -m "Message" /path/to/file1 /path/to/file2
Add a new file
cvs add /path/to/file
cvs commit -m "Message" /path/to/file
Show the differences between two revisions of a file
cvs diff -r 1.23 -r 1.19 /path/to/file