You work on one Group at a time by opening the slider for that group. You change the permissions in the Select New Settings drop-down list boxes. The options for each value are Inherited, Allowed, or Denied. The Calculated Setting column shows you the setting in effect. It is either Not Allowed (the default), Allowed, or Denied. Note that the Calculated Setting column is not updated until you press the Save button in the toolbar. To check that the settings are what you want, press the Save button and check the Calculated Settings column.
The default values used here are the ones set in the Global Configuration Permissions Tab