Impero, by default, doesn't allow staff members to add users to groups.
This is an option that has to be enabled by admin members via Impero Server settings.
If the option is disabled, the staff member will have a blank area in the group's properties (right-click on a group>Properties).
Note: you can't add any new member to the Entire Network as it already contains all the users.
To enable the feature, log into Impero Server.
Move in Settings>Console Access Rights.
Select the user/computer/group that will need to add users to groups.
Under the Access tab, scroll down under Risk Management and enable Add users to group by name
The selected user will now be able to add users to groups by selecting [Add New Member], Import Users or Directory Import: