How does one go about attending an auto auction?

You see them on TV and I'm sure they are held all over the place, but how do you actually participate in one? I've heard that you can walk around a lot full of cars, but to attend the auction itself, you have to be part of some double super secret organization?|||You can go to any public auction. And most of them are free.|||Maybe it depends on the auction, but I would think you could show up early to look at the cars and anyone can participate. I know when I used to go with my Dad you just had to register your name and you got a numbered paddle to hold up.