I use Play and I have never had coverage problems. At least for calls and SMS'es. It might be different with mobile internet (in the past it was so, I have no idea how it is now). But for calls and SMS'es it's perfect. If you don't like Play, other operators also have such offers, but i case of most of them you have to pay something every month - here is quite an old comparison of such offers: gsmonline.pl/artykuly/roczna-waznosc-konta-na-karte (in Polish)
In Plus GSM: plus.pl/uslugi/rok-waznosci-konta
- you need any pre-paid SIM card and at least 10 PLN on the account (it will cost 10 PLN to start this option)
- you use the code *136*11*18#
- you charge your account with at least 5 PLN within 30 days
Then your account is valid for a year.
I recommend pre-paid rather then post-paid, it's just cheaper in most cases.
Do e gave something like x ninety of free SMS and x number of free calls in a month?
Yes, it's usually so that you can make calls and send SMS'es up to the level of your monthly fee. Often you have some SMS and calls more for free, or even totally for free (to the same network, to all mobile phones in Poland or to all the phones in Poland).
I'm afraid you must try to use Google Translate and study Polish versions of their websites.
Pre-paid is "na kartę", post-paid is "abonament", "mix" is something in between (either you sign a contract that you will charge your pre-paid account regularly with for example 30 PLN for a month - it's so in Plus and Play - or you pay a monthly fee based on a bill and you can make calls and send SMS up to this fee without any extra charges - in Orange and probably T-Mobile, although I am not sure about the last one; but in any case, if you use it up, you can charge your account like with a normal pre-paid).