To understand how the Citi Secured Mastercard works, it helps to know the difference between a secured versus an unsecured credit card. A secured card is designed for building or rebuilding credit and requires a refundable deposit. To get a Citi Secured Mastercard, you must apply and get approved. Then you must make a deposit of between $200 and $2,500. The amount you deposit will be your credit limit, which is the maximum you can spend on the card.