chown arsham file.name

chown -R arsham directory.name

chgrp new_group file.name

owner-group-others

ls -l

drwxr-x--- 17 arsham home      4096 2007-04-29 11:17 documents

Giving read permission to owner :
chmod u+r file.name
Removing read permission from owner :
chmod u-r file.name
here u means user ( owner )
Giving write permision to group :
chmod g+w file.name
Removing execute permision from others:
chmod o-x file.name
Giving read permision to all (owner+group+others) :
chmod a+r file.name

read = 4
write = 2
execute = 1

read + execute = 4+1 = 5
read + write = 4+2 = 6
read+write+execute=4+2+1=7

rwx-wxr-- : chmod 734 file.name
rw-rw-r-- : chmod 664 file.name
rwxrwx--- : chmod  770 file.name
rwxr-xr-x : chmod 755 file.name
rwx------ : chmod 700 file.name
and so.....

chown arsham:home file.name