Players are given colored stones they need to shift around in order to group all matching colors together (adjacent, no diagonal). Your baby brother could do that, but throw in the fact that stones are limited to a handful of moves indicated above and the game gets a lot harder. Swap two stones, and the numbers for each go down by 1. Stones with 0 are un-movable and a show stopper.
Once you get all the colors grouped with matching colors (meaning all reds next to reds, and all blues next to blues) you win the level! Again, sounds simple, but as the game progresses it gets more and more challenging. Early boards will start out as 3×3 squares with two colors, and will eventually grow to a mind melting 6×6 and five colors.