A Show N Go is usually set up at a training facility, and run just like a dog show class to get you and your dog in a show type setting, doing what would be expected in the ring.
Around here, we have agility, rally, and obedience show n gos. In agility ones, you get a certain amount of minutes to run the course, or train. In obedience, they go through all of the exercises you would do in an obedience trial, and in rally, they set up a rally course for you to run through. You are generally allowed leashes, treats, and toys, if needed.