At the end of the auction you will receive an invoice for your purchases by email.
After you log in, go to "My Purchases" menu to see a list of all purchased items.
By default you will see a list of items pending payment. Check the "Include Paid Invoices" checkbox at the top right of the page to view all purchased items.
Click the "Print Invoice", or "Print Receipt" (for paid items) button for a printable invoice/receipt document.