Screen recordings are great. If a picture is worth a thousand words, than a quick Youtube video is worth a thousand pictures.
The best free screen recorder for macOS is Quicktime. It's built-in to the OS, and it's free.
The main drawback of Quicktime is that it doesn't record the computer's audio output.
But there's a way to fix that.
You can use Soundflower to redirect the audio output of your Mac back into Quicktime.
Download and install it from https://github.com/mattingalls/Soundflower -- be sure to right-click or control-click the installer.
Once you've installed Soundflower, you'll be able to send audio to it. Select it in the output section of the audio preferences, or the drop-down menu for your volume control.
And now you can select Soundflower as the audio input when you make a screen recording with Quicktime.
It works great. Here's a Youtube video demonstrating the process:
Not bad, eh? A free macOS screen recorder, with audio too!