This is John Conway's Game of Life, a cellular automation that exhibites several very interesting effects. There are two types of cells: dead and alive. And there are only two rules: (1) any dead cell that has exactly three neighbors comes to life, and (2) any living cell with less than two or more than three neighbors, dies. The two rules are applied to create new "generations". When you reload this animation, you can observe many patterns. Some configurations stay put and never change, others go back and forth between two configurations, and some slide across the map. Some can completely dissapear and others can continue growing forever. See this video by Veritasium for some interesting discussion.