It is not. There is a set amount that you are provided. For adults, that stipend is limited to the first few months, but past that they are expected to find work to support themselves. For minors such as yourself, there is a stipend and housing provided until you turn of age, though that too is limited to a set amount per month to cover your living expenses. Because this funding must also provide for everyone who comes through the halfway house, there are limits to how much they can provide for each resident. If you'd like extra spending money, you are welcome to apply for a work permit.
The numbers on the card are the number to your account (that's the long serial number) and a security code (that's the short one) for verification that you are the cardholder when making purchases when you aren't present, such as online. You should not share those numbers with anyone unless you are purchasing something from them, and if you lose your card please be sure to alert the DA employees at the Halfway House immediately.
Ling, it's very important, for your benefit and protection, that you have a thorough understanding of such practices and policies. I strongly advise you to come to the Halfway House Community Center when you have a chance. They are staffed by experts that can help you learn more about the technology and practices of this world.