Collaborating on Documents is by far one of the best features of using Google Drive. Colleagues can develop documents, spreadsheets and presentations, collaborating on a single document in real time from different computers anywhere in the world. They can contribute to the document synchronously and asynchronously. Using the 'revision history' you can evaluate contributions to documents as well revert back to an earlier version.
When a document is shared and more than one person has the document open, there is a notification at the top indicating how many viewers are in the doc with a drop down list identifying who each viewer is. You can also see what they are editing while they are doing it in real time.
Comments are often used as a 'proofing' and 'feedback' tool for collaboration. Teachers use comments to 'correct' drafts. Colleagues use comments to ask for clarification or make suggestions without making changes to the actual document.
Insert a comment
1. Place your cursor to the point in the document you want to comment on or highlight the text.
2. Click on Insert>Comment
3. Type your comment.