Shushan Purim is the 15th of Adar on the Hebrew calendar and celebrates like Purim the victory over the Persian empire. Shushan Purim is celebrated the day after Purim becuase their was continued fighting in the capital city of Shushan one day later than the other fighting and thus the Shushanite Jews celebrate on the 15th of Adar instead of the 14th of Adar. The day commemorates the Jewish people being saved from death from Haman around the fourth century BCE according to the book of Esther.
People will listen to the Megilla in in effort to experience the story told in Esther, Haman and Mordecai. Some will twirl graggers and stamp their feet when Hamans name is mentioned. It is also a day to give to the poor. Food and other gifts are calendar to help those in need. Some areas will celebrate with carnivals that involve costumes, and festive games.
Back in the times of the Persian empire, Haman the royal vizier to the King Ahasuerus planned to kill all the Jews in the empire but the plan was stopped by Mordecai and his adopted daughter Esther who had risen to become Queen of Persia.