Have you played Plants VS Zombies? This is the same thing. You don't want the monsters to reach the other side of the board or else they will eat your catnip. Click and drag the cats to bring them out onto the board. The cats will try and deflect the monsters but they still sometimes come through. In the beginning of the game, it is sometimes helpful to use the $$$50 cat. It will deflect all monsters.
Thanks to Alec and Faye who taught me how to program.
