Due to electronic banking, most of the conveniences of home are available to you on post and in most large cities. You may keep your Continental United States (CONUS) checking account or establish one at the base bank or credit union. Some people keep one in the CONUS and one overseas. Just keep in mind the mail delay in deposits made to CONUS banks. Your paycheck has to be electronically deposited and most travel payments and other payments from the government can be electronically transferred. But other deposits may have to be mailed. An ATM card (automatic teller machine card) is very useful here as everywhere and can often be used in major cities of most countries. The ATMs and banks/credit unions on base can give you both dollars and host nation currency.
You will find you will use cash much more on the economy than you probably did in the CONUS. Although many stores and hotels take credit cards, they are not as commonly accepted as in the US. If you need a check in a currency other than dollars, say to buy furniture, the post bank or credit union can provide one for you for a nominal fee. The post banks can change currency for several nations. If you want large quantities or something other than local currency, you may have to order the specified currency a few days in advance.
Generally, you get better exchange rates in the country of the currency so it's often a good idea to wait to buy lira until you're in Italy and pounds in England. It's easy to find currency exchanges, in airports and train stations, banks and offices specifically for money exchange. Depends on where you're going however and how much time you will have - it's always a good idea to get some currency in advance, for the cab driver, cup of coffee, or whatever before you have a chance to hit the exchange facilities. You cannot buy currency for many of the former Eastern Bloc countries until you get there since there is no international trade at this time in Czech, Polish, Russian, or similar currencies.
Whoever is changing your currency is not doing it for free -- avoid buying too much and converting back because you will lose money in the process. It's common advice but still good -- DO NOT exchange money with street moneychangers. There is an excellent chance you will be cheated.
Go here to find Foreign Exchange Rates