Can someone please explain waitlist?

I have seen several posts about waitlist, but I don’t understand the procedure. I am trying to get tickets to take my daughter for her birthday in New York. But these resale prices are pretty steep. Is waitlist and option for New York as well and if so, how can I get on it? I saw people mention it for LA. Any help is appreciated thanks. I will also call the box office to see if I can get tickets.