From Game Editor
Activation events are sent directly to specific actor from another actor. To add an activation event, right click the actor, and choose 'add activation event'.
It will prompt you for an event to use as the trigger.
You will then see a rainbow line from the actor to your mouse; click on some other actor to assign that activation event. Press esc to cancel or finish selection.
Then, in the other actor that you just clicked on, in the actor control panel, add an event > activation event. It will ask you for the actor to recieve the event from.
You can then enter any event or script to be performed when the event is received.
Examples of usage are a start button, that triggers the view to move to the gameplay area, or sending the onscreen buttons in modern touch devices to give the player an event when pressed.