It really looks a lot like a socket on an extension. You put the end of it over the rod, and you have the SDS Max set for hammer mode. They squeeze the trigger and it drives the rod on down into the ground. When going through landscape timbers, I've had no problem going four feet through five pre drilled timbers without any effort on my part. It will end with about an inch of the rebar still sticking out of the timber, but that's really easy to finish off with a sledge hammer!!!
Amazon.com: Milwaukee 48-62-4091 Ground Rod Driver: Home Improvement
Eddie