You have time to spend a few hours in the city! Take the AirTrain from the terminal to Jamaica Station and transfer to the subway into Manhattan. It will cost you $5.00. The trip in will take about a half-hour to 45 minutes, depending on where you want to go.
Look at the subway map to see where you want to go and which line(s) will take you there. The subway is pretty easy. You should allow 1.5-2 hours to get back through security, etc when you come back to JFK. Have fun!
You have time to spend a few