Card Number is the 16 digits across the front of the card, Exp Date is the 4 numbers divided by a slash below after the 'valid thru', your CVC is the final 3 digits of the number on the reverse of the card after your signature box.
Select mastercard from the card type when asked, make sure you use your full name as billed to along with your billing address.
Once you enter all this, if you choose to save it, during future transactions you will only need to re-enter the CVC in order to process your transactions.
Enjoy your RIOT points.
Edit: Sniped by Hohums. Curses foiled again!