Open your Google Doc
Select the text, image, or object you want to comment on
Click the Add comment icon in the toolbar
Right-click the selected item and choose Comment
Use the keyboard shortcut Ctrl+Alt+M on Windows or Cmd+Option+M on Mac
Type your comment in the comment box
Click Comment to post it
To reply to a comment, click Reply and type your response
To edit or delete your own comment, click the three dots on the comment
To resolve a comment, click Resolve on the comment thread