All around the globe cash machines, also known as ATM machines -- have become more and more common. Very often, these cash machines will be the best way to exchange your money, but you should verify the tourist information website for the country you're visiting to confirm you can use one there.
Before you leave for your trip, make sure to contact your bank. The majority of foreign ATM's use 4 digit pins and use numbers not letters. You want to make sure your card will work abroad, and you want to alert the bank as to where you will be using it. If they suspect any unusual activity, they may put a hold on your card. They do this to protect you against fraud, not to make things hard on you... so give them a call, and let them in on your travel plans.
It is ideal to take a couple of cards that you can from different banks to use at the ATM. This gives you a backup in case a machine can't read one of your cards or if one gets demagnetized. Money is usually available in the local currency, so figure out the exchange rate ahead of time... and calculate how much you want to get. You can get the exchange rate before you leave by checking online at a currency converter like OANDA. In the airport Arrivals Hall, there will almost always be a bank as well as a cash machine. The bank will have conversion rates posted so you can check before you use the machine.
ATM's in some countries give you high denomination bills. You're going to need "little money" sooner or later, so it's a good idea to go to a bank as soon as you can and get smaller change. If the banks are closed, ask your hotel to change at least one note into smaller ones.
Your ATM card has a cash limit per day, and you can't exceed that. Some foreign banks may may have a maximum withdrawal that is smaller than you want. And, because you will be charged a fee, so it pays to take out $200-300 at a time instead of $20 each time you need a little.
Use your ATM card for debit rather than as credit. However, if you do use a credit card, remember that it is considered a cash advance, and you will be charged even higher fees.
If at all possible, try to find ATM machines that are in an enclosed area instead of just open on the street. If you must use one on the street, make sure it appears safe. Be alert and aware of your surroundings just as you would using automatic teller machines at home. Once you get that money... protect it. Put it away as soon as you can... preferably in a money belt. Once you have money in your pocket and more in a safe place.... enjoy your vacation!