Click on the Add comment ( + ) icon on the toolbar.
Insert your comment on the pop-up comment box.
Click on Comment to post.
Now everyone who has access to the file will be able to see your comment assigned to the highlighted text.
Note: After the comment has been addressed click on Resolve to dismiss the message.
Mention
Users can mention someone in a particular section of a Drive file to catch their attention. Assuming the file is shared, follow the steps given below to mention someone.
Locate the file you would like to take this action on.
Highlight the text where you want to mention someone.
Click on the Add comment ( +) icon on the toolbar.
Press "+" and enter the email address of the person you would like to mention.
Click on Comment.
This will send out an email to the mentioned contact adding them to the discussion.
Note: After the issue or comment has been addressed click on Resolve to dismiss the message.
Assign
With the help of the assigning feature users can assign tasks to members who have access to the Drive file. Assuming the file is shared, follow the steps given below to assign a contact.