That wooden box is around a pan of soy milk, which is cooking on a hot plate built into the table. There is another high-tech control panel built into the side of the table to control the hot plate. When the soy milk begins to boil, it makes a skin. Then you use chopsticks to twirl that skin into your bowl. That is called "yuba". It is then flavored with various seasonings (different from one serving to the next). If if doesn't form a skin as fast as you want to eat it, you can fan it with a special fan the waitress gave us.