Question about external auto tuner

I have an LDG RT-100 external antenna auto tuner for my vertical and I wanted to know how I was supposed to ground it. The instructions tell me that I need to connect it to the antenna ground system, so what does this mean exactly? Do I just stick a rod in the ground and connect it to the tuner's ground or somehow connect it to the base of the antenna? This might be a stupid question but grounding things never seems to be cut and dry to me.