Adding a group to a Linux directory

Adding a group to a Linux directory

On my Linux server I have made a group called emtbackup and added user1
and user2 to it. Also user3 created a directory called dbbackup so the
path looks like this:
/var/www/vhosts/mysite.com/httpdocs/dbbackup
How do I add the group emtbackup to dbbackup directory with rw rights? The
end result should allow all 3 users to read, write to dbbackup directory.