How to Set up a Trigger to Start a PowerPoint Animation
Open the element’s drop-down list on the Custom Animation task pane and choose Timing.
The Timing tab of the Effect Options dialog box displays.
Click the Triggers button.
Triggers options appear at the bottom of the dialog box.
Select the Start Effect on Click Of option button.
Trigger start options display.
Choose the element on your slide that you will click to start the animation.
The elements on your slide are listed in the drop-down list.
PowerPoint places the trigger icon, a trigger finger, next to the animation that plays when you click the trigger element. Triggers on the slide are listed in the Custom Animation task pane.