You can multiple contacts to a customer and export this information whenever you want.
Select View Customers from underneath the Invoices & Receipts tab in the main menu.
Search for the customer you want to add a contact for and click on their name or the edit icon on the right hand side.
Select the Contacts Tab and click the Add Button.
You can then enter all the contact information for the contact and click Save to add it to the database.
To Export all your customer contacts just select the contacts tab and click the Excel button towards the top right.