Screencast-O-Matic is a screenrecording app that is built into Canvas. It is available as a tool called Studio via the More External Tools menu of the Canvas editor (Figure 1).

Figure 1. The More External Tools of the Canvas editor

Following that, you will be asked to download some software. Do so without fear. Once Studio is installed, launch it and prepare for your capture session (Figure 2). Your first task is to:

Ensure that the region of capture is NOT full screen, but one of the smaller built-in defaults (1080p or 720p). These correspond to the typical movie formats which will be the final destination of your screen recording.
Arrange whatever it is you are capturing so that it is clear and well-framed within the region of capture. get rid of unnecessary material.

Figure 2. Arranging the region of capture and 'setting the stage'

External learning resources

There are lots of good tutorials on Screencast-O-Matic's website. The most useful ones in my opinion are:

A quick intro the the screen recording editor is here
An overview of how to edit audio post-capture
Animating a zoom (very useful for zooming in and out of points of interest)
How to add text
Scripted recordings!
Adding transitions between clips