Basically it does just want it says. Get a juice, any 100% juice with more than the required amount of sugar per serving, drop in the powder, place the supplied air seal on the bottle, and wait two days. In return, you'll get a nice bubbly drink that tastes similar to mixing whatever juice you used with a hard cider. I used white grape, and probably should have picked a hardier variant. It would be a great drink for a party punch bowl (since it's relatively inexpensive per serving), or a hot summer day.
One thing to note, when you've reached the desired fermentation, remove the yeast from the bottom. If not, it will continue fermenting, even if you put it in the fridge. I did this by pouring the juice on the top into a pitcher, and leaving the sludge in the bottom of the juice bottle. Just wash it out, and put the juice back in, and you're set.
Also, be sure to keep the airlock on the bottle once it's in the fridge. Don't use the bottle cap! Since the yeast is still doing its job, if you use the bottle cap, pressure will cause an explosion.