Richard provides a pretty thorough explanation of the site, and I’d encourage you to go to his post to read about it. A quick summary is that it teachers can create virtual classrooms, students can read and annotate tons of materials the site already has (and teachers can upload their own, too – including webpages), and teachers can embed questions they want students to answer. And it’s free (you can pay for a premium service, but what it offers for free works for me).
I’ve embedded a video below that provides a short overview. One other great feature of the site is that it has tons of videos clearly explaining how to use each of its features.
I’m adding this post to: