With your contact/member, you can add notes. When you add a note, you are given the option to make a note available to the member. If you make it available to the member, assuming they have access via the membersarea permissions, they will have the ability to view these notes/comments.
You can also check the box to Send Update via E-mail to Contact. If checked, a copy of the comment will be sent to the contacts e-mail address on record.