How to make a video presentation with a video of the slideshow and a video of me speaking in the corner? I am a teacher and I am trying to sync my slideshow presentation to a video of me speaking about the slideshow presentation. I'm trying to make it so that the presentation takes up most of the screen, and the recorded video of me speaking takes up a corner just outside of the slideshow area.

I have a Mac, so any suggestions with mac-based programs would be preferable. 

Thanks
Preferable depends... But possibilities are for example: MacOS offers the App iMovie which is available with no further cost. For more professional video editing you can use e.g. Adobe Premiere or Final Cut, but then you need to pay and you need much more effort doing research to get familiar with it. To sync two videos and the iMovie App will be fine.