On page 47 of the eBook it says:
By default, commenting on the profile content type is enabled.
On the content section of the profile panel page (/admin/
build/pages/12), we can simply add:
• “Node Comments”
• “Node Comment Form”
If we rename the titles to “My Wall” and “Write on my wall”, we
have a wall-system already in place.

My question is: how can we "simply add Node Comments and Node Comment Form?