Literally I have no idea how to proceed with this, so I want to go for and accounting office in Krakow to get it done.
If you are working on umowa o prace (standard contract) haven't change the employer in 2012, don't have any additional incomes, don't run a company etc. It's a piece of cake... at least for somebody, who knows Polish... you should get PIT11 at work and you basically write it down into PIT... 37 (as far as I remember) and check If you need to pay/get back anything... unless accounting department at work screwed up something, there should be nothing more to pay... you can bring it completed to the tax office and person behind the desk may scheme it to check if it is correct... and that's it... for a Polish speaking person it's a matter of 15 minutes, better buy a beer someone from work to get it done for you or ask accounting people, If they employ foreigners, they should help with it...no need to spend any extra money.