In almost all the levels (the game has more than a hundred) you will have to protect a certain attack zone from your enemies. To defend said zone you will need to place your pokemon in different squares on the map. They can attack any enemy that passes close by their square. That way they can defend the zone using their attacks.
With this simple approach you will have to fight dozens and dozens of battles. The main attractiveness is that when you advance in the game you can capture new pokemons and raise their levels. The higher their level, the more damage they do, the more life they will have and the better attacks and developments you can unlock.
Pokemon Tower Defense is a game that mixes strategy and role-play in a masterful way, combining all of it with the brilliant setting of the Pokemon world. Even the graphics will be liked by the fans of the saga.