You may enter personal notes about a client or a case.  For entering personal notes about a client, click on "Clients" tab, select the client in the left side list. On the right side pane, click on "Client Details/Edit" and then click on "Personal Notes" link.

Similarly, for entering personal notes for a case, click on "Cases" tab, select the client in the left side list.  On the right side click on "Edit Case" tab and then click on "Personal Notes" link.