Kami is a digital classroom app that allows you to transform any existing document into an interactive learning experience. Students can use the built in tools to write over the top of (annotate) documents that you share with them in google classroom.
The Kami website is located at kamihq.com
To get your students started with using Kami will depend on if you have the free or the paid version. I will describe the process for the free version and make mention of what the paid version brings to the table at the end.
At the heart of the Kami experience is the Kami Chrome Extension which can be added by going to the Chrome Web Store. School managed chromebooks may restrict this feature so your tech department may have to add the Kami app to the whitelist or push it out to student chromebooks.