A quick search of beer can chicken on the web will provide more information than needed. So, I won't detail the process here. Basically, the chicken cooks from the inside due to the liquid as well as the outside, so it's a quick way to cook the entire bird on the grill. The can doesn't need to be a beer can, and a soda can was used on this round. And the liquid doesn't need to be beer. This can had some lemon juice, water, rosemary, and garlic in it.
We do have the stand that makes this a bit easier and my advice is to get that. It prevents a potential burn, so well worth the cost. In fact, we bought two stands since making two chickens isn't twice as much work. Although we didn't make two this time it does make sense to have more chicken in the freezer for quick meals.