what is it you want to know, rp? I do know that in the US, you can check up to 2 bags not to exceed 25 or 30 kg and you can carry on one bag along with a personal item like computer or purse....once you are in the EU or Poland, the regulations are different....you can only carry on one item.
Flying from Poland to England, I was charged 300 zloty for excess baggage (can only check one and total weight if you have more than one cannot exceed 20kg----I was charged for having to check an extra bag (it was to big for me to carry on) and the total wt of the two bags was 28 kg, so I was charged for excess wt also. I was flying on Wizz Air, and since it's a no frills airline, their policy may be different from other airlines.
Flying back to the states, I was able to check 2 bags, but still could only carry on one item....