How to Comment on a Google shared Document
Steps
(1) Open the document you have been asked to collaborate on by clicking on Open With (top menu) and selecting Google Docs
(2) Click on the Comment Button in the top right hand corner of the Menu
(3) Select Comment (next to Notifications)
(4) Type your comment in the box provided
When you finish your comment, Click on the Comment Button (blue) to post your information on the document.
(5) If you would like to receive notifications of when others comment on the same document, click on Notifications and select All
NOW YOU ARE COLLABORATING ON A SHARED DOCUMENT!!!!