Pokémon Ranger's gameplay is much different from any other Pokémon game out there. Being a game specifically made to support the Nintendo DS's release, it focuses much more on the use of the touch screen and the stylus, making its gameplay and the game in general a very unique addition to the franchise.
To put it in summation, this game is based around drawing loops with your stylus around Pokémon to capture them. Once captured, Pokémon will follow you around and can be used to help clearing obstacles or completing objectives. Different areas contain different Pokémon to find.
Being a Pokémon Ranger, your job is to help the people around the region of Fiore. People will provide you with different missions and quests for you to complete with the help of Pokémon, as you also attempt to stop Team Go Rock's evil plans.