permission to a single module

[Nic]

Hi to all,
I am new to the use of CVS.
How can I set to a USER a write(commit) permission to MODULE-A and 
readonly permission to MODULE-B and forbid read and write permissions to 
othe modules ?
I read a lot of documentation and FAQ, but so far I don't have solved 
the above permission problems.
If you can address me to a complete documentation, I'd really appreciate it.
Thank you in advance,
Nicola