Unfortunately, credit cards don't start out with any money on them. When you use a credit card, you are actually making an agreement with the credit card company to borrow the money today to buy the item and then promising to pay the credit card company back at a later date.
Credit cards have a thing called a credit limit. This is a limit based on how much the credit card company thinks is the most you can spend. As you get older and pay your bills on-time, your credit limit usually goes up. For a college student just starting off with a credit card, it will usually have a limit lower than $1,500. Older working people who have paid their bills on-time for 15+ years can have credit limits greater than $25,000. But, remember, just because you have a high limit doesn't mean you should charge that much onto it. In order to avoid paying interest, put things on a credit card that you could afford to pay for at the end of the month. If you don't, a $1,000 purchase could actually cost you $2,000 in the end!
Money Smart Kid