This plugin has very nice interface for managing site page permissions. You can change permissions from Admin Interface by clicking Permissions link.
Please note- For Group and Sub groups Permissions I have added separate pages.

1. This page shows all controllers list with their functions.
2. By default plugin do not check permissions for Admin. You can enable permissions checking for admin from All Settings page.
3. If you want to give any page permission to public/guest then select Guest group of required function of controller in list and save it.
4. Here you can set and unset permissions for any group.
5. This plugin checks permission on each and every request.
6. This plugin makes a cache for fast checking permissions and does not hit database each time.
7. When you change any permission from Permission page it deletes the cache automatically.

I have added Permission Chart for better interface to give or revoke permissions.