For those of you unfamiliar with the concept, the cone of vision is basically what is in your range of vision based on a cone extending from your eyes. In photography, we often refer to this as the angle of view or field of view, but it's much the same. In general, what that means is that when looking straight ahead, how much you can actually see in front of you of the overall scene, horizontally and vertically. Also worth noting that the cone doesn't mean everything is in focus, that degree of focus your vision is actually quite narrow, around 2° or so.
In any event, Dan does a great job explaining the concept and how to get it set up in your work: