Create a Group under an existing Group
 

Hi, I want to create a fresh group under an existing group, is it possible. How to.............Thanks.

As in you want to create a group that inherits rights from another group above it, but also has its own set of specified rules? Sorry to answer a question with a question but I'm just kind of clarifying so I know what I'm looking for.

I don't understand the question, perhaps you're trying to make another group that has same user that are already on other group?
If that so, there isn't any group inheritance (that I'm aware of) so what I would do is to make a new group and add members to it, since a user can have many groups besides it's initial group

as root:
changing users an groups names as needed

If the suid bit is set on a directory in Linux, if you create a file in that directory, the owning group of the file will be inherited fron the owning group of the directory. The default group of the writer will be lost however. You might want to look at the setfacl and getfacl programs. You can add permissions for several groups or owners.

setfacl -m user:jim:r filename
setfacl -m user:jane:rw filename
setfacl -m group:netgroup:rw filename
setfacl -m group:labgroup:r filename

You can shorten user to u, group to g and string -m entries:
setfacl -m u:jim:r -m u:jane:rw -m g:netgroup:rw -m g:labgroup:r filename

Thanks...therefore, I want to say, there is already existing a group "Mkt" (Marketing), now I want to add a new group "sales" into "mkt" group. Is possible...........thanks

Groups don't have group members. There are no subgroups.