First click the "New Email" button in the top left of the outlook client. In the new email field click the "Address Book" button (Under the Message tab).
You will then be able to search for a staff member or scroll through the list of all staff members.
Once you have found the staff member you want click their name and then the "To ->" button. You can select more than one staff member.
That staff member will now appear in the "To" section of your new email.