1. Select the Insert tab on PowerPoint
2. Select Screen Recording and then select whether or not you want to:
3. Select the area of the screen you want to record (i.e., do you want to record the whole screen or just a portion?)
4. Select the record button
5. Select stop button when finished
This video, by Don Leitch, shows you how to create a screencast using PowerPoint 2016 on a Windows machine.
This video shows how to record a screencast using a Mac. The Mac version of PowerPoint does not have that function built in. Once you have recorded and save the screencast, that video can be uploaded into a PowerPoint slide.