Working with split screen technique

At first I didn't understand how to use the split screen on Imovie, however when I discovered how to use it, there where complications such as some shots in the film where cut of, so you couldn't see some of the important shot in the film opening. When I started to cut some of the shots to shorten the length  of the film opening. The shots that where cut off by the split screen where discarded and there where no more problem with the split screen. Overall I found working with the split screen technique difficult at first, but after a a while it became easier and more enjoyable.