Law /
Registration as a Sole Trader in Poland [21]
There are probably 50 threads here already about that and I would suggest using the search function. However.
Basically, you need to go to the town hall and fill in a form specifying the types of work you want to do. They can't refuse any more to let you do this. They will give you a piece of paper. You need to take that to the tax office and fill in a form specifying the method of bookkeeping you will use and giving a bank account number. Contrary to the advice that some tax offices give, you don't need a separate bank account. You also need to go to the Main Office of Statistics (GUS) and get a pointless number called a REGON. Another bit of paper. You used to need to take that back to the tax office and may still. The final thing you need to do is to register for social insurance (ZUS). You will need to either be registered at an address (this ends soon) and/or have a document from the owner of a property giving permission for the registered office to be there.
The order in which you need to do these steps has changed over the years and there are certain inconsistencies from city to city but basically the town hall is the first step and the ZUS is the last step.
You may find it easier to pay someone to do all this, however it is worth mentioning that the people who do it for money don't always do it either well or quickly and may give you incorrect information. If you do it yourself, you may find it easier in a small town rather than a city. I did it once in Warsaw. The whole process took just over a week and involved a lot of waiting and a lot of pointless form filling. Keep all documents.
You need to complete all these steps in order to get the rubber stamp made up, without which you won't be able to issue a bill for any work done.
A correction. Re. a tenancy agreement, as far as I remember it doesn't need to specify commercial use however it certainly mustn't contain a clause forbidding it. Even though registration at an address ends soon, there will still be a need to prove your right to operate a business from whatever address you give. If you have a friend with an office, they can give you a (signed and stamped) letter to say you have permission to operate from that address, however that letter is for the tax office which may put some people off doing it.
If you are not a citizen of an EU member state, there may be further complications about proving the basis of your presence in PL. I had to do that before but not after Poland's EU entry. You will, in any case, find out during the process.
The order in which you need to do these steps has changed over the years and people here have reported certain inconsistencies from city to city. I did it twice for myself in Warsaw and a couple of times for other people. The whole process took between a week and involved a lot of legwork, form filling and waiting in queues. It also obviously needs to be done in Polish. You will also need to show photo ID like a passport at each stage.
Be aware that bureaucrats in Poland are not known for either consistency or efficiency and in the dozen or so years I have been here there have been numerous small changes in the way they interpret the rules. The tax office is by far the worst and you may find that on Monday you are told one thing, on Tuesday you are told the opposite and on Wednesday you find that neither are correct.
Be aware that you may (and almost certainly will) be given conflicting advice by people who say they are 100% certain the are fit. This is normal here. I can confirm that the steps above were correct when I did it and I doubt there have been more than minor changes since.
Good luck and enjoy!