Google has nearly all you need to learn Slides! Check out the organized content in the Google Workspace Learning Center.
Additionally, the Google for Education Teacher Center has some resources!
Navigate to Slides.Google.com.
Expand the "Template Gallery" (top-right).
Select the "General" tab (more than just EPS).
Explore, select, and customize a template!
SlidesCarnival: free Google Slides themes for your presentations
SlidesMania: free Google Slides themes for your presentations
slidesgo: free Google Slides themes for your presentation (set the filter under "License" to "Free" to view the FREE ones) Note: Must create an account to receive 10 free templates per month.
Templates and Ideas to create cool things with Slides & Drawings
Caption This! A fun, deep-thinking Google Slides or Google Drawing Activity
from Kasey Bell ~ Shake Up Learning