Add a new group:
/usr/sbin/groupadd hello

And then add user to new group:
/usr/bin/gpasswd -a <username> hello

After modify the ownership of a folder/file in Linux by
chown -R root.hello /home/hello/shared

other users that is in the group of hello, must re-login to gain the access permission.

Reference:http://www.redhat.com/docs/manuals/linux/RHL-7.3-Manual/ref-guide/s1-users-groups-private-groups.html