Using the Video editor
Zoom in or out of the timeline
Use the pinch-to-zoom gesture to change the timeline view. Pinch out to zoom in or pinch in to zoom out within the timeline.
Move or delete a clip
Touch and hold clip, then drag it to a new location (or to the trash can to delete it).
Trim a clip
Tap a clip to display the trim bars. Drag the trim bars to shorten or lengthen the clip.
Transitions between clips
Tap the transition
effect icon 
between
clips to select a transition effect and duration to insert.