Scrub the timeline
Scrubbing refers to manually scrolling through an animation, forward and backward, previewing your animation, pausing where you like in case you want to add a keyframe.
To scrub the timeline
Select the timeline from the Storyboard picker by clicking the Open a Storyboard button under Objects and Timeline and then selecting a storyboard.
Click and drag the playhead as you want, forward or backward.
As you drag the playhead, you will see the animation play out on the artboard.