Original: The story of Metroid II follows the protagonist and playable character Samus Aran, who is sent on a mission to exterminate the Metroid creatures from their home planet SR388 before the antagonistic Space Pirates obtain and use them.
Simplified: Samus Aran goes to a planet called SR388 when the Galactic Federation told her to exterminate the Metroids that live on it. After exploring the underground areas of the planet and killing almost every Metroid, she fights and kills the Metroid Queen.