The Address book will allow users to search for any person that is in your CRM system and get their email address.
This appears in the email compose window and appointment compose windows.
Click the button to open the dialog
Type some text to filter the data
Click on the row to add to the current selected field (TO, CC, BCC)
TO is selected by default
To change click on the field EG CC and then click on the row to add it
Finally click OK to see added to the compose window