The Mouse Events require the user to perform an action with the mouse (or touch) to trigger all the actions inside.
A Mouse Down Event will trigger the actions as soon as the mouse button is pressed.
Trigger Property
You can choose how to trigger the event, either on the object the event is added or anywhere in the scene.
Here are the different Actions you can trigger with the Mouse Down Event:
Transition ActionAnimation ActionSound ActionParticlesVideo ActionOpen Link ActionCreate Object ActionDestroy Object ActionSwitch Camera ActionScene Transition ActionReset Scene ActionSet Variable ActionVariable Control ActionConditional ActionClear Local Storage Action