Play around with the text, and try to comment. Don't worry, you can't break anything.
To edit a document, just click the 'Edit content' button. Now you can click anywhere on the text and start editing it, right here in your browser.
Saving your changes is even easier. Just click 'Save Changes', and you're done! This demo won't actually save your changes, but you get the idea.
Gone are the days of reviewers writing "on line 155, ...", leaving you to search - now they can just comment right next to the paragraph. Do this by hovering your mouse to the left-hand side of the element you wish to comment on.
You'll also see some speech bubbles with numbers in them next to certain paragraphs. This means others have commented on those paragraphs already. Simply click on the speech bubble to view the comments.