It's been a while.. but we were shown two different methods of finishing. Both start with the dog sitting in front as was mentioned....
In the first method the dog would move to your right and circle around you until they "finished" in the heel position. A lot of the beginers and their dogs seemed to prefer this method.
My favorite though was the other method. My dalmatian did this type of almost automatically from the very beginning. I start this on leash and again with the dog sitting in front. I very rarely use treats in my training because I hardly ever have a way of carrying them when out walking and I don't want my pup to rely on me having them to do what is commanded. Treats are for tricks is my motto hehe. Anyhow... as corgimom said you would take a step back with your left leg, somewhat pulling your corgi towards your left side as you do. Corgi should stay on your left side in this method... come towards you on the left... looping towards you. As your dog hits the back of the "loop" you would bring your left leg back to a comfortable standing position... which should encourage your corgi to finish the loop back to a heel position. In this method the dog does not actually circle your body... as all the work is down on the left side.
Honestly, I hardly ever use "finish" (which, by the way, is one of the commands you could use after your dog has mastered it without a leash).. and have not even tried to teach it to Checkers yet, but if you would like to try competing in obedience classes you will need this.. and it can be quite fun and impressive to show off to friends too
.