The On Show trigger allows you to trigger an action whenever an object becomes visible, whether it is by a specific Show action or when the page on which it appears has appeared on screen.
Note:
This effectively allows you to trigger actions automatically without any action by the user.
Add the On Show trigger to your Actions Organiser, as described in Creating and Editing Actions.
Click on the Actions tab in the Actions dialog to select an action or actions to add to the trigger.
Go to Choosing an Action to list all of the actions you can add to your trigger.