If you’ve created a Keynote presentation for your class, you can add your own narration to it, for your students to hear. Keynote can record not only your remarks, but also the timings that you use as you advance from one slide to the next.
The video below will show you how to make the recording. When you’re done, you can save the presentation as a video file, which will require no special software for viewing. Then you can upload your finished video file to your Moodle site.