[Mediawiki-l] Create a new group and add users to it?

[Tech Geek]

Hello Folks,

I am using MW 1.15.5. By default the following groups are present on my Wiki
(Special:ListGroupRights):
all, Users, Autoconfirmed users, Bots, Administrators, Bureaucrats

Now I would like to create a new group called "managers" and add few users
(for example john, tim and rick) to that group. How do I do this?

Thanks!