The Edit Page : The Project Editor : The Timeline

The Timeline
The Timeline features a video track, audio tracks, the Time Ruler, and the Playhead. You can scrub through the project by swiping left or right on any of the tracks. Tapping on a clip moves the Storyboard to its location.
You can also use horizontal “pinch-open” and “pinch-close” gestures to zoom in and out of the Timeline, which is useful when you want perform tighter cuts or trimming.
 
The Time Ruler and Playhead
The Time Ruler is marked in hours, minutes, seconds and frames, starting at “00:00:00.00.” When you tap the Play button, the Time Ruler moves from right to left past the Playhead, indicating where you are within the project.
The Video Track
In addition to reflecting exactly what's on the Storyboard, the Video track is where you will perform various editing functions such as trimming, as described in Editing Your Project.