Go to Business » New Client to create a client and then fill in the contact details. They will automatically be included when you create an invoice for this client.

Note: If you already have a list of clients, Fanurio can import them. Go to File » Import to import one or more clients from a CSV (comma-separated value) file. Most applications (especially e-mail applications) can export their data to such a format. A wizard will assist you along the way to make things easier.

Note: On Mac OS X you can import your Address Book contacts as clients from the File » Import menu.