Pardon my ignorance, but I've never done an international flight. I have an upcoming trip which takes me from SFO to Nairobi by way of EWR. The itinerary is all United, but there is a plane change in EWR to a Swiss Air flight. Will I go thru customs when I leave SFO or am I supposed to do that in-between flights in EWR? The trip is still about a month away, so I don't know any gate assignments yet. Thanks everyone!