The applet initially starts with a very simple shape called the r-pentomino. This simple pattern quickly evolves to spread throughout the "world" following the basic rules of the Game of Life. If you click inside the applet area a new random pattern will be created.

The rules:

• If a cell has less than two living neighbors, it dies.
• If a cell has more than three neighbors, it dies.
• If an empty cell has exactly three living neighbors, it is born.

This seems pretty simple, and perhaps somewhat morbid, but in reality this small set of rules creates systems that are extremely unpredictable and dynamic.

More informaion can be found here