This first video shows Screencastify. If you are recording on a Chromebook, make sure Screencastify is set to Save to Google Drive and untick the "Pause on low disk space" box.
Here is one way to use Screencastify to record a Google Slide Presentation.
If you'd like to use Snagit, make sure you install both the Chrome app and extension. The video will show you how.
Have a question? Check out the How-to page at USD Technology Resources.