Here is an illustration of the peppered moths. Notice how the light-colored variety stands out against the dark tree trunk, unlike the dark-colored variety to his left. As you would expect, the light colored moths are more easily seen by birds, resulting in more of them being eaten, eventually resulting in the dark variety being predominate. That is all natural selection is – nothing complicated – just the expected consequence of how well a particular trait leads to increasing the chance of survival and therefore the leaving of more offspring that are also likely to possess this trait.