That's the great thing about American Express. It is a recognizable name associated with thousands of online stores and brands. It is preferable to transfer your US Dollars into a more usable form if you have funds in a less accepted payment form. To find out more about where you can use American Express, just visit their website. To make a purchase, just enter the card number and security code, as well as the expiration date. The merchant will then authorize the payment and the funds will be deducted from your total, just like a normal credit or debit card.