The Permissions tab contains information about:
All available project permissions Permissions
All project actors Actors
Permission matrix Matrix
View by Permissions
View by Actors
Permission Overview
This sections shows:
The assigned Permission Scheme
Number of People added into the project
Actors (number of roles which used in the permission scheme)
Granted permissions / Total permissions
Permission Matrix
This sections shows:
All available permissions as rows
All available Actors (Users, Groups, Project Roles, etc...) as columns
Permission matrix which displays
 when an Actor has the permission
View by Permissions
This sections shows:
Every permission as a row
Actors in the 2nd column, if they have the permission
View by Actors
This sections shows:
Every Actor as a row
The obtained Permissions in the 2nd column