The easiest option for Mac users is QuickTime, the built-in screen, webcam, and audio recording software in the MacOS. 

Quicktime icon

How to use QuickTime Player from apple Support:  

Alternatively, Mac users can also download the apps SnagIt or Screencast-o-Matic with similar features. 

SnagIt Screen Capture

SnagIt Home Page:


Screecast-o-Matic Home Page

VoiceThread is another free tool that is more of a presentation-style option. It is not a screen recording tool, but it is a tool that allows you to build and record a presentation within it, using slides you've created that you can navigate through. 


VoiceThread Home Page:

Finally, there is a Chrome browser extension called Screencastify that can record anything within the browser, such as a Google Slides presentation or a Prezi. 


Screencastify (you must be using the Chrome Browser to install and use this tool)