Google Doc Help
Please choose the suggesting mode in the top right 
You can then make editing changes to the text and it will automatically track your suggestions, which I can then accept or reject. 
If you wish to comment, select the word or section you want to comment on, and then move your cursor to the right margin and a comment box will appear. 
You can then “talk to me” by making a comment (rather than a change).
Don’t forget to click the “comment” button to save your comment.
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