Ereshkigal is the queen of the land of Kur, which is to say the underworld. More specifically, the city at the center of the earth where the souls of the dead reside.
Even more specifically, the souls of the dead the the “seven who decree” (literally, the Anunnaki – four land gods and three sky gods) petition Ereshkigal to enter her kingdom, and assign a corresponding stature / importance depending on how much the soul pleased the Anunnaki in their life. There was also a strong ancestor worship component of existence in the underworld where a soul earned their place (remember, this is a culture with a caste system) in the underworld through their actions in life, but kept their position through the prayers and offerings of the living. More specifically, it was the duty of a family to keep the spirits of the dead in the high (un)lifestyle they earned through devotion and sacrifice.