Confirm that your credit card has a cash advance option. Virtually all MasterCard and Visa credit cards offer that option, but a store or gas station credit card might not. Call the number on the back of your card to inquire. Also ask how much available credit you have for cash advances.
Request an ATM PIN for your card, if you don't already have one. You can get a PIN by writing or calling your credit card company.
Take your credit card to any bank ATM machine. Insert the card and use your PIN to withdraw cash, just as you would with a debit card. Or take the card inside the bank to withdraw funds at a teller window. The teller can process the cash advance by using his teller machine. He will swipe the card, wait for authorization and have you sign a receipt. Your signature will be compared with the signature on your card and you may be asked for additional identification, such as a driver's license.