How do you get on The Ellen or Oprah Show during the giveaways?

[Orange Peel]

Its obvious the audience knows theyll be getting tons of stuff before they do by how they act. And its obvious theyre getting more than they paid for in tickets:

So how do they get on the show? Im sure its some kind of lottery system or something? Or are the tickets just sold by first come first serve? If so, then people would sell theirs on ebay for more money esp. during a giveaway event? And then you would give a motley crew of random people in the audience, which isnt the case as all the audience is pretty much middle-aged females all the time in the ellen show.