If you are a manager in the Manage Contacts role you can add a contact via the address book via the + button in the Action menu.
Any new contact created on a lead will automatically end up in the Address Book and if you have integration with a DMS or CRM system these will also appear in this screen.
It is also possible to 'Import Listings' using a preset format. If you don't have the format you can 'Download Template' from the 'Import Contacts' screen.