Customer AccountsCustomer Accounts\Maintain Customer AccountMaintain Customer Account\Customer Invoices

To see and work with all invoices associated with a customer, select the customer then from the maintain customer screen, click on the Invoices tab to gain access to all of the selected customers invoices

 

From the invoices tab, you can double click on any invoice to open up an invoice and work with it.  In addition, you can also select an invoice and click on display order to open up the order Associated with the invoice.