What you get in the pouch is this slab of fluorescent yellow gel/putty. It seems to have some kind of alcohol in it, but doesn't list that on the outside. You basically take the slab, lay it on the keys, and moosh it in. The mooshing seems to help it clean the key sides somewhat. Slowly peal it back, and it will have grabbed any loose and lightly adhered keyboard grunge. It seems to do a good job of cleaning the key tops and an OK job of the key sides. If you really push it in, it also grabs the stuff below if it's not too deep.
What it won't do. Remember when you ate Cheetos and typed your term paper/business report/extended coding session? You know that stuff that is on your key sides you have to scrape to get off? Won't touch that. Nor will it fix the sticky drink you spilled in.
Depending on your level of risk aversion, you can try the dishwasher trick (for separate keyboards only, not laptops). Just be sure to not use a caustic soap (look for something that says "Safe for silver") and dry completely.