This is a very simple game. There are five different animals and five different colors. One deck has a card with each animal in each different color (25 cards). These are spread out on the table.
The other deck is different. On each card there are four animals in four of the five colors. So for each of these cards, there's one animal and one color missing. The game is to be the first one to figure out which animal/color combination is left out, and then point to the proper card from the other deck.
An adult can help a young kid along by hinting about what color and letting the kid figure out the animal or vice versa.
The game develops some good skills for pre-readers, and my 3.5 year old daughter really likes it, but it's more like playing with flash cards than a game. Sure, you can keep score if you wish, but there really isn't a winner or loser. Two or more young kids could play against each other with some adult supervision, so it's got quite a few positive aspects. I certainly thought it well worth the price.