how do people send questions to the show?

I don't think you actually send them directly to the actors.
In the ones I have heard of, the guy conducting the interview (be it directly fox or any guy with a tv, radio show...) ask via his website, twitter and/or facebook at his followers to send him questions and he choose which one he will ask.
So you actually have to stay tuned and send your question to the right person at the right time and hope for the best.