Then use Apple iMovie's picture-in-picture tool, insert your commentary over the clips. The Mac computers make the process easier by having a built in camera. Activate that, speak your mind, and the on camera segment goes directly into your iMovie editing project.
If you've not used iMovie and are interested in learning how, check out this video tutorial I produced.
Here's a new three item "Quick Takes" I put together featuring basketball, green space and GoPro cameras!
Here's another example: GOP candidate Donald Trump's campaign manager gets in hot water for grabbing a reporter trying to interview Trump. The clip is only 11 seconds and you have to watch closely- and a few times- to see the incident. I looked the clip several times to go with my commentary.
Here's a link to a third example of this project. I did this three topic "Quick Takes" in Fall 2015.