I’d battled this question long enough without a good answer. I know there is documentation out there that spells this out easily, I just needed something verbal and visual that I understood to get it all to make sense for me. I could never remember who had the ability to publish posts or who had the ability to add a plugin. So, I went ahead and created something that made sense for me in my classroom.
I took the five WordPress user levels (Subscriber, Contributor, Author, Editor and Administrator) and made a handout with descriptions of each and screenshots of what each user level can see on the backend. After a few years I think I have things straight now. Hope you can find the handout useful as well.