Group Permissions

I understand how to create a group and add users to it, but what I want to be able to do is to set group level permissions.

For example, I want the following groups, in order of importance:-
Trial Member
Member
Moderator
Class Leader
Officer
Admin
Super Admin

The trial member group (which is what I want all initial sign-ups to be in by default) will only be able to post in 1 forum, read news articles etc.
Obviously these ranks will have varying privileges up to Super Admin, which of course has full rights to everything.
I also want each rank to be able to see/use forums and features beneath them, but not be able to access those above them.

For the life of me, I cannot seem to find where to define these rules.

Any help would be appreciated.