Click the flag to draw. Change the 'Size' slider smaller to zoom out. The 'wait' slider is how many hundredths of a second it waits before each step. The 'Wait To Draw?' slider toggles if it draws after each step, or only after a whole bunch of steps. (That can help reduce lag if the size is small.)
So what is this? Well, here's the story: There's this guy driving a limousine. He's really famous, so wherever he drives, people build a street. (At the beginning, he starts in a single city block.) But his limousine is so long that he can't turn at the street corners; he can only turn in the empty space. So he goes straight the whole time he's driving on streets. How does he decide which way to turn? He's a bit weird. If he's in empty space, he will always turn (except when there's streets so close that he doesn't have any place to turn anyway). Every time he switches from driving over empty space to a street, he changes his mind on which way he wants to be turning (left or right). It might be helpful to set the 'wait' slider high and the 'Size' slider high and watch to get a better understanding of that. This is an idea I came up with and then programmed in Scratch to see what would happen with it. I tried different starting configurations of roads, and they all make a big city that either goes up/down or left/right. (Maybe he designs it after the shape of his limousine!) You read all the way down here?