chown, or CHangeOWNer, is really, really easy to use. chgrp is even easier. There are only a small handful of switches, only two of which are commonly used, and only three arguments to the command.
First, the switches:
-R this sets recursion -v this sets verbosity
As for the arguments, well, you can either set the user only:
chown username foobar
set the group only:
chown :groupname foobar/ -or- chgrp groupname foobar/
or set both at the same time:
chown username:groupname foobar
That’s pretty much it. Don’t forget the recursive switch if you need it.