I want to go from Costa Rica to San Francisco, but there is a connection in Charlotte. So, should I put both of those flights on the form, or just the one I take from CR to Charlotte? Same accurs in the departure flight.
The arrival flight is the flight number of the flight which first lands in the US having departed from another country. So this will be the flight which lands in Charlotte. (Example: AA1706)
The departure flight is the flight number of the flight which takes off from the US and lands in another country. (Example: AA1707)
Don't worry if you have to change your itinerary later. These are used in part to verify that your proposed itinerary makes sense with the rest of your application.