I auditioned 3 years ago. Me and a buddy went, we are both comedians.
We waited for about 7 hours, got to the interview process. Basically a 60 second interview with a random person who works for the show. They asked me my name, asked me if I had any kind of interesting back story, then asked for a small sample of my act. It was a little awkward since you are in this really loud room surrounded by other people auditioning and people waiting to audition, but I managed to get a couple of jokes out and made the guy laugh.
They called me back a few weeks later but I didn't have the means to get to Dallas for the second audition so I missed out on it unfortunately.
My advice is to come up with some kind of gimmick or sad back story. My buddy told them he was gay and had a falling out with his father because of it, neither is true. Plus of course if you have an agent and can get a private audition that is totally the way to go obviously.