Lots of useful information about money stuff and some interesting history. First - check whether you have new Polish zlotys or old Polish zlotys. If you have old - keep them as a souvenirs since they are worthless, even the millions.
Poland currency is "zloty" (zl.). 1 zloty = 100 groszy. Polish coins have values: 1, 2, 5, 10, 50 groszy and 1, 2, 5 zloty. Polish banknote (paper money) have values 10, 20, 50, 100 and 200 zloty. Now inflation is 10-20% per year in Poland.
Exchange money offices called "kantor" are in almost all Polish towns. A tourist can find them easy usually in the center of the town. Their exchange rate is better than in bank or in exchange "kantors" in the airports. Do not exchange money on the street, you are in the risk receiving false money and you are an easy victim of rubbery or pickpockets. Banks also exchange travelers check with commission 1-3 %.
Credit cards are not that popular in Poland like in some other countries. Many shops and smaller and cheaper restaurants (called "bar") do not accept credit card. Credit cards are accepted in many hotels, luxury restaurants and travel agencies. Generally, credit cards (Visa, Eurocard/MasterCard) are accepted more in big tourist towns than in the smaller towns or in the country.
Do not keep all your money in one place. Distribute them in several pockets. Do not show that you have lots of money in any way on the street.
Some history of Polish zloty:
In eighties the inflation in Poland was very high - 100-1000% therefore the prices were reaching astronomical (very high) values in zloty. During hyperinflation everybody in Poland was a multimillionaire since the monthly salaries were equal a couple of millions zloty. But the unofficial course of dollars was so high that the value of monthly salary was equal to about 20-30 dollars. Since 1995 the "new" zloty was introduced. The value of "new" zloty was equal to 10,000 "old" zloty. For two years these two currencies "old" and "new" zloty were in circulation.
In communistic times there were two courses of dollars. One - official and one black market rate. The official course of dollar was much lower than the unofficial but only limited amount of people traveling abroad were allowed to exchange limited amount of zlotys into dollars. On the other hand the foreigners from Western Europe and the USA were forced by Polish government the exchange a certain amount of money into zloty while visiting Poland of course according to much lower rate than the black market course.
In seventies a chain of shops called "Pewex"was created. In these shops everything was for sale but only in dollars and so called "hard currency" (currency which could be exchanged into dollars). One can imagine a frustration of Polish people because "Pewex" stores looked much more attractive and have much more products than the regular stores. The prices of majority products in "Pewex" were very high for the average Pole. The only exception was Polish vodka which price in zloty was kept high in order to prevent people from excessive use therefore it was more practical to buy vodka in dollar store. For some time the amount of vodka sale from "Pewex" was so significant that its price regulated the unofficial exchange value of zloty and dollar in Poland. Hopefully these times are gone and would never come back. Check the articles: Solidarity times, Polish economy.
The current exchange rates of zloty into dollar can be calculated using a free Yahoo Currency Converter service . Many tips about "money stuff" with pictures of present images of Polish bank-notes are in the webpage TravelPoland.com. Check also whether you have old Polish zlotys.