usergroups on navbar

[pureturk]

I want a link on the navbar called usergroups or groups whatever its called.

and each member maybe upon registration or after registration to choose a group.
the groups for instance will be Irish, Hungarian, Greek etc.

and when you click on the usergroups thats on navbar, it will show all the groups along with all the users that belong to each gruop.

how do I accomplish this?