As with the Java implementation of the Glider Gun, you may Stop, Start and Step the animation.
The red squares are "resting" and can not be populated until the next generation.
The initial state is random. So here we see a completely disordered random system becoming ordered.
Clicking on Setup will produce a different random initial state. And each different initial state will evolve very differently.
But each system will sooner or later evolve into an ordered state unless all the cells end up empty. So we see that the rules determine the behavior.
With the Brian's Brain rules, there are many more gliders -- and many more types of gliders -- than with the Life rules. In fact, almost everything ends up as a glider. Glider guns are also very common, and they themselves are gliders. And if you watch carefully, you might even find a glider-gun gun.