Poland has its own currency – Zloty (PLN). There are both paper money and coins in circulation.
Current EUR to PLN rate is around 4.3 (1EUR equals ~ 4.3PLN).
You can exchange money at the airport in special points or withdraw in multiple ATM’s available in the city (few ATM’s in Złote Tarasy and nearby).
Credit cards are widely accepted in Poland. Most common systems are Visa and MasterCard. Amex is rarely accepted.
Some smaller points might require minimum spend of ~10PLN (~2,32EUR).
Tipping is not obligatory, you can tip whoever you want to show that the service was good. The average tip is around 10-15% of the cheque. For bigger groups in restaurants ~10% of service charge might be added to the bill.