Please note that in some cases it is required to obtain a VISA before entering Poland.
If you are a citizen of an EU member state
the only thing you need to have to enter Poland is a valid travel document or a document confirming identity and citizenship (i.e. your national ID).
The two main documents you will need to enter Poland you if are not a EU citizen
- a valid travel document (passport);
- a visa (if required). Generally, you need a visa to enter Poland. There are, however, a number of countries that are free of this requirement. For more details refer to: https://www.gov.pl/web/diplomacy/visas
Poland is a part of the Schengen zone, so you can apply for a Polish visa and travel all around 27 countries it covers. Basically those are most of the EU countries, except Ireland, Romania, Bulgaria, and Cyprus. Although not members of the EU, countries like Norway, Iceland, Switzerland and Lichtenstein are also part of the Schengen zone.
Here you'll find instructions how to get a visa in 5 easy steps: http://www.go-poland.pl/visa-application
using e-consulary https://secure.e-konsulat.gov.pl/
Please note that the process of obtaining a visa can take several working weeks!