This video explains and shows the new features found in the iMovie 10.1.3 update released in October 2016.
Full changelog from Apple about what’s new in iMovie Version 10.1.3:
• Support for Touch Bar on MacBook Pro lets you quickly add video clips to your movie, or use them to create picture in picture, green screen, and split screen effects
• Tap the Touch Bar to play your movie, split a clip, or easily adjust the volume of any clip
• Ability to delete render files to recover drive space