Screencast-o-Matic has been my favorite screencasting tool for years. I use it on my Windows and Mac computers to create almost all of the videos that you see on my YouTube channel. The one knock against Screencast-o-Matic has always been that it wouldn't work on Chromebooks. That has changed. Last fall Screencast-o-Matic launched a beta product that worked on Chromebooks. And yesterday that product left beta and is available to anyone who wants to use it.
To use Screencast-o-Matic on a Chromebook just go to this page and click "launch recorder." You can record your screen or your screen and your webcam simultaneously. You can narrate your videos by using your Chromebook's built-in microphone or by using an external mic like a Blu Snowball.
There is a free version and a paid "pro" version of Screencast-o-Matic. The free version will let you record for up to 15 minutes, record as many videos as you like, save to your Google Drive or local drive, and use your webcam while recording a screencast. The pro version removes the time limit, removes the Screencast-o-Matic watermark, enables cursor highlighting (that yellow circle you see on my screencast videos), enables drawing tools, and enables access to the offline editor. The pro version costs $18 a year. If you use my referral link you can save 20%.