Adobe Spark is a great way to create video with a Chromebook. It is simple, scaffolded, and works. 8th grade students at my school are currently using it for Social Studies, but it could be used for many applications.
Here are my tips for getting started with Adobe Spark Video on a Chromebook. Full video above, but my tips are linked below by topic.
Finding and Inserting Pictures: Start 2 minutes in.
Creating Map images with Google Maps to insert: Start 5 minutes in.
Starting to record your voice overs : Start 6 1/2 minutes in.
Downloading and Sharing: Start about 7 minutes in.