Players begin the game with one Pokémon, and can capture more using Poké Balls. They can also use their Pokémon to battle other Pokémon. When the player encounters a wild Pokémon or is challenged by a trainer to a battle, the screen switches to a turn-based battle screen where the Pokémon fight. During battle, the player may use a move, use an item, switch their active Pokémon, or flee, although fleeing is not an option in battles against trainers. All Pokémon have hit points (HP); when a Pokémon's HP is reduced to zero, it faints and cannot battle until it is revived. If the player's Pokémon defeats the opposing Pokémon (causes it to faint), it receives experience points. After accumulating enough experience points, it will level up; most Pokémon evolve into a new species of Pokémon when they reach a certain level. Less