If the event is not part of a group calendar, a user will need the Full Write Events permission to perform these actions.
If it is part of a group calendar, a user will either need to be the group admin, have Full Write Groups, or Full Write Events permission to perform this action.
Adding guests to the Guest List
Each event allows you to construct a Guest List of who is expected to attend. These can be entire groups, individuals, and even people who don't have a profile in the system (i.e. external guests and event registrations).
From the "Attendance" tab within a group > Logs sub-tab > Select the "Update Guest List" button.
The Update Guest List pop up will appear. If the event is part of a group, all current group members will automatically be added to the Guest List. Also, if the event requires registration, sign ups, or if the event has check-in enabled, these members are automatically added to the Guest List.
To add groups ( 1 ) search for a group to add its members to the Guest List.
To add people individually ( 2 ) search by the individual to add them to the Guest List.
External guests can also be added ( 3 ) who do not have a profile in the system.
Remember to "Save" your changes.