I'm interested in buying Ultimate Game Cards for Crossfire, but I've never used them before, so I don't know exactly how they work (I don't have paypal or a credit card that's why I'm using this option).

What I want to do is buy 100k ZP (Total: 110k (With bonus)) for $79.99, but from what I've seen cards generally sell for $10 or $20 each (Maybe more?) So say I buy four $20 game cards, then I redeem them one by one will the ZP automatically be bought, and put into my account? Or is there like a balance where all the money redeemed from each card is saved, stacked, and stored, then I buy the ZP myself?

Basically, I want to know how to use UGCs for Crossfire, so that when I do buy them i don't waste hours trying to figure out how to get them to work.