The extra wire acts as an extension that goes one one side of the grounding block or the other, whichever is more convenient. The grounding block is that metal block with a coax in and out, and the ground point. You then run the ground wire to a electrical meter, using that corner clamp, or if you have a water pipe going in the ground you can clamp it to that. One or the other, not both. I have linked a diagram to display this.
Mike
