First, you need to start a new save. You can change the grid size, edge type, etc, but keep the grid type on the default setting. Once the world is loaded, food (green) and critters should begin spawning. Press the down-pointing arrow next to "microscope", and select "simulation settings". Then press the down-pointing arrow next to "settings simple", and go to "neuron settings". Press the arrow next to "general", and select "input neurons". Untick everything, and then go to "middle neurons", then untick everything. After that, go to "output neurons". Untick everything but "jet", "dna copier", "membrane maker", and "mouth". Then press R, and come back to the game after about an hour. Repeat untill you can see a large black spot (or any large, black shape in general). You can then disable "creatures random" from "settings simple", and optionally, enable most neuron types that you disabled.