LifeSite Pro allows you to make internal notes about your client (or about anything, really.) To be able to make a note, your client must have already created an account and accepted your request to access his or her account. You can not make notes about clients whose invitation statuses are pending or declined.
To make a note, click on the "Notes" button next to your active client's name. An empty box labeled "Update Client Notes" will pop up for you to enter in text and save notes.
These notes are only viewable to you and can range from personal reminders, to notes about the names of your clients' pets, or any other bit of information that you want to have recorded and accessible at all times.