Polish currency is złoty (PLN). 1 dollar is approximately 3.1 zlotys and 1 euro is approximately 4.2 zlotys. To obtain current rates, you can use currency converter.
There is no problem to find exchange ("KANTOR" in Polish) in Warsaw, but you probably won't get good rates at the airport. The other possibility is to withdraw zlotys from an Automatic Teller Machine ("BANKOMAT" in Polish) - Visa and MasterCard are widely accepted. Many shops and restaurants accept most widely known cards as well.