If you are an EU citizen you can enter Poland on the basis of your ID document (or other valid document certifying your identity and citizenship). For stays exceeding 3 months you are obliged to Register the Residence in Pomeranian Voivodship Office in Gdańsk. It is free of charge.
Documents required to register residence:If you come from a non-EU country you can enter the territory of Poland on the basis of a valid passport and a visa (if required). You have to obtain the visa from the consulate of Poland in your country.
For stays exceeding 3 months or before Polish visa expires you are obliged to personally apply for a temporary residence permit in Pomeranian Voivodeship Office in Gdańsk.
Documents required to apply for a Temporary Residence Permit:For more details, please visit Pomeranian Voivodship Office website: http://www.gdansk.uw.gov.pl/en/