Hello folks, I'm new to spiceDb. I read some example and document in your github and did try the playground. However, I feel not confident on that. Do you have any system that can be an exercise for me? Thanks for your help.

In which aspects do you not feel confindent? What kind of "systems" would you like to see? Have you checked our "protecting your first app" docs? https://authzed.com/docs/guides/first-app