1.to create group info,hr,sales
2.three user for three group(total 9 user )
3.Each user passwd is [passwd]
4.each group has certain directory the group member are acces, not allow another
5.one user will be member of all group and acces thair directory.
6.certain group of members modify thair file or directory.

plz help me.

Hi,

You will need to get your hands to command line and use "chown",

If it's like this:
+ you have a "info", "sales" ... with users:
- ann
- bob
- chris

which need to create/ modify the files in their "shared" directory ?
How to add users to group?
You need to create that shared directory and allow them doing things they need.
this will create "info_shared" directory and allow users in group "info" to write.

How will you share the directory it's a more complicated way,
you can do it with Samba
or if the users will be using the "server" to login, they will be able to browse the directories on the "server" (in this case you are done).

this looks like homework. regardless, please give us some context (including what you have read on Linux and BASH.)

One excellent reference:
http://tldp.org/LDP/Bash-Beginners-Guide/html/