I booked my flight back in May before I got my passport, am I supposed to call the airline and give them my passport info or do I wait and show them my passport at the gate?
Either way it's ok. You can log onto the airline website and enter the info there with your confirmation number. You can call their customer service and give them your passport info. You can wait till 24hr before departure and check in on line to enter your passport info. You can check in at the airport and hand them your passport.
I don't know if this is true for the USA, but for flights from the UK into France you are always required to supply your passport number in advance. It doesn't seem to happen with other European countries.