Google Slides presentations are super easy to add into your course using the multimedia lesson type - you just need to find the correct link to use so that it's just the slides that are displaying (and none of the editing stuff that comes up when you use the usual Google sharing links).
Here's how to find the correct link:
1. In Google Slides, select File > Publish to the web...
2. Select 'Embed' (edit your playback settings if you like).
3. Then select just the URL part of the embed code - that will be anything between the first set of speech marks after <iframesrc=
4. Copy-and-paste that link to use as the URL for your multimedia lesson.
And that's it!