How do you  use a green screen on imovie?
 Begin by opening iMovie and click on Preferences. In the General tab, make sure the Show Advanced Tools is checked. Now film your video with your green screen. Then import the video(s) onto your computer from your camera. In iMovie, click on File, go to Import and select Movies.Place the video(s) in your project. Drag the green screen clip onto the project clip. When the menu pops up, select Green Screen. 