Most exchanges will not allow you to use a pre-paid debit card. The original concept was to create a substitute of the conventional currency that at the time, seemed to be elusive in the crippling Financial Crisis. However, when clients use credit cards in purchasing Bitcoin, they elude the monitoring system as credit money is usually legitimate, they then service their loans with the laundered money and the cycle continues. It allows limited access of nodes on the Bitcoin blockchain for small BTC transactions. CEX is only available in some US states; please see this page for details. The FAQ section below should answer all of your remaining questions.