To leave a comment on a file, click the comment bubble at the top of the individual file preview page.
Type a comment and hit enter. The owner of this file, and anyone who was invited to collaborate on it, will get a notification email that you have left a comment. They can reply to your comment, leave their own comment, or mute the email notifications at any time.
To mute or unmute email notifications, click on the bell icon at the top of the comments area. By muting notifications, you will no longer receive an email notification when a comment or reply is left on that particular file.