Online test is like 30 questions in 15 minutes. You don't get to know your score.
You do well enough, you get invited to an in-person try out. They hold those in various cities, and you have to get to the one closest to you. I was luck I just had to jump on the train to get to mine. (There are like 12 cities they go to, and I don't know how many people are invited. I was in a classroom sized group of about 30, but there were groups before and after my tryout of the same size.) At the tryout, you take another test, and then you play a mock game -- this was 4 years ago, so the process may have changed some since then.
Even after all that, they tell everyone in the room that they may be eligible for a taping, so wait for a call sometime in the next 18 months.
Then if you get the call, you have to make your way out to California, and pay for your hotel. They had a discounted rate where they had a partner with the hotel, and they ran shuttles from there, but it still cost me about 1000 bucks just in travel and lodging (I was unemployed at the time so that was huge).
Then you go to the taping -- they do a week's worth of shows in a day, and I think a whole month's worth over the week. Even there, you are not guaranteed being on the show. they had an alternate come when I was there, but they let California people be the alternates so that when they were called back the trip wasn't too bad.
You play some practice games to get used to the board and the stage and the buzzer, and so that they can get your mark with the camera. Then you go back and names are drawn for the games. I was drawn first, and never got into a groove. Got second, but nailed the final answer.
Prior to the taping, they ask you for a lot of prompts for the contestant interview. No one is interesting in 20 seconds, especially when the most interesting thing about you now is that you were on a major television quiz show.
I got second and won 2K. It was nice, but I hated the time frames. The initial test was in January, then the call for the second test was in like April for a May test. Then I was called the next February for filming about a month later. The episode didn't air until late July, and then I didn't get the money until that November.
It was worth it, but it is one of those things that a lot of people are interested about but I have over-told the story. It makes me feel like a band with one hit song.