Google Drawings is like the old Paint program. Use Google Drawings when you want to elicit a creative response for any subject OR when you would like to provide a graphic organizer for students to complete to reflect or guide their learning.
Google Slides is a presentation tool, but it can be "hacked" to mimic templates from social media and other websites. You might also use Google Slides in your course as an announcement to include your agenda for each module/folder as a checklist for students, directions, and links to other items needed. Slides can be an excellent hub to collect links to resources.