Members of EU countries do not need a visa to enter and stay in Poland up to 90 days. For period longer then 90 days, they have to legalize their stay by applying for a Temporary Residence Permit at local Immigration Office. This has to be done a short time after arrival in Poland. A Temporary Residence Permit entitles you to stay and work in Poland. The Universities will help you with the application procedures.
Students from outside the European Union need to apply for a long-stay visa (for whole period of study) before entering Poland. The short-stay visa is valid for 3 months and can only be extended once, in case of emergency. Long-stay visa allows you to stay in Poland without applying for the Temporary Residence Permit. Contact a Polish consulate or embassy in your country of residence for complete details of the application procedure.