Once your webshop has been configured with test Auth keys, you can make a test purchase using AfterPay as the payment method.
If you want to test the whole chain, ask your Implementation Manager for an Auth key to the Afterpay Client Test environment. You can use this in Test mode. You will receive confirmation emails, and will be able to see the invoices in MyAfterPay, the customer portal used for payment and invoice management.
Once you and your Implementation Manager are happy that everything is in order, you will get a Live Auth key, and can start offering AfterPay to your customers!