Screencastify is a great extension that is available in the Chrome web store. It will allow you to create videos or screen casts. Instead of using Screencast-o-matic on my laptop, I wanted to use my new Chromebook. I downloaded the Screencastify extension and created my short video in minutes! It was quick and easy to learn. Here is my short, 'how to' video on reserving, editing, and deleting an event on a Google Calendar.
A great feature to Screencastify is that once you complete the video you create, it saves it in a folder called, 'Screencastify' in your Google Drive.
I would highly recommend downloading this extension and trying it. You will not be disappointed!