Previewing and scrubbing let you see and fine-tune your animation as you're working on it. The animation preview and scrubbing tools only show animation; events in the Events track are not triggered.
Previewing your animation
As you're creating your animations, you can see how they look on the stage by clicking the Play 
Quick mode: The preview playback starts at the scene whose thumbnail is currently selected in the timeline. As each scene plays, its thumbnail becomes highlighted.
Advanced mode: The preview playback starts at the playhead position if it's within the preview range, or at the beginning of the preview range. The playhead moves along the timeline while the preview is playing, indicating the current point in the animation that's showing.
Preview range (Advanced mode only)
By default, the preview range is the full length of the animation for the current page. The start and end of the preview range are indicated by markers in the time track at the top of the timeline, displayed as two pairs of small yellow triangles. If the end marker is at the end of the animation, its position automatically updates to the new end point when the animation lengthens or shortens.
To view the preview range, hover over one of the markers. The range highlights in yellow.
To adjust the preview range, drag the start or end marker to a new position along the timeline. The timeline snapping setting applies. You can also double-click a marker to move it to the beginning or end of the animation.
Loop the preview
To loop the preview playback, select the Repeat play 
Looping the animation preview vs. looping a layer
- Looping a layer changes the animation. The animation for that element will loop in the published document.
- Looping the animation preview causes the preview playback on stage to run through the preview range continuously. The final published document is unaffected.
Scrubbing (Advanced mode only)
Scrubbing lets you see how a particular segment of your animation looks on the stage as it plays forward and backward at a manually controlled speed. To scrub your animation, click the top of the playhead and drag it back and forth over the part of the timeline you want to test.