Go to shipment manager in ppobox account
Enter new shipment.
Enter all details.
Once package is created you can see a button to upload invoice in created shipments.. Upload the invoice and done.
Once it is received by ppobox warehouse in US it will be shipped on the same day or the next day and they will send you a notification. Once its received in india they will send you an invoice of total import charges and a link to pay. Once paid they will dispatch it to the recipient address mentioned while creating a package in your ppobox account