If you have a driver's license from another country, you don't need to have an International Driving Permit, but it is useful. The permit verifies in multiple languages that you have a valid driver's license. Police officers who cannot read the language of their foreign driver's license will be able to read the permit.
OK good. Now, regarding valid driver's license. Can I use my Pennsylvania learner permit to drive in New York
Yes, but you must obey any restrictions imposed by the state that issued your permit and any New York State rules in place.
And what do I do if you intend to return to your home country and need my international driver's license?