Updated: Mar 17
By default anyone with Admin user rights will be able to access all events in EventHQ. However when you were setting up your new users you may have chosen not to check the box to give them access to all events. In this case in order for that user to be able to access an event you will need to grant access to them from the event.
Having the ability to define your own user roles and then access to specific events gives you complete flexibility and total control over who can do what.
(If you have watched the video on how to add a new user please note I have unchecked the access for Ad Min to see all events this is not a system error)