Assuming the subject says it all, check out man 8 adduser.  It'll tell 
you the proper procedure.  You might also want to check out the FAQ and 
related docs for a few useful references on unix:

http://www.macbsd.com/macbsd/macbsd-docs/

I hope this helps.

Later.

-- 
Colin Wood                                      ender@is.rice.edu
Consultant                                        Rice University
Information Technology Services                       Houston, TX