You can collaborate with your colleagues and clients by creating conversations and write comments and at the same time include files you want to share. New comments will automatically appear as unread comments in the Conversation window, where you can reply.
Collaboration in the portal
Conversations as seen from WorkBook:
Conversations as seen from the Customer portal:
Private comments: when you add a new comment, you have the option to reply privately. You only need to use this option if you have your customers working in the system through the Customer portal and you want only your internal employees to see your comment. Private comments are only shown to employees.