You need to be more specific: what region, what kind of labour.
The national currency, and only one valid is Polish zloty. Euro could be accepted too, but it's just making fuss as it would be converted from zloty to get euro and then you would convert it again to spend the money here in zloty, so you'd loose twice some % on exchange rates.
Wages start from around 5.5 per hour, but all depends on kind of work.
General rule is the salary is paid monthly in Poland, however, your contract should describe everything.