trigger a animation

When you add an entrance animation, it runs whenever the object starts in the timeline. However, you can make it run via a click with this method: 

• Create the object and set it at the beginning of the timeline.
• Add the desired entrance animation to the object.
• Set the object's initial state to Hidden. 
• Use a trigger to change the object's state to Normal when the user clicks another object (or when something else happens).
  • When the state changes from Hidden to Normal, the entrance animation will run.

Unfortunately, there's currently no way to trigger an exit animation. Those just run at the end of the object's timeline. 

When you add a motion-path animation, Storyline automatically adds a trigger that runs the animation when the timeline starts. You can edit that trigger so it runs when something is clicked (or something else happens).