The worship of Devi Durga in the month of Ashwin is called 'Akalbodhan'- an uncoventional time for inauguration of the worship. It is so called since the period of this worship differs from the conventional period (during the spring - 'Basanta' tract:
In the ancient times, a demon called 'Mahishasura' earned the favor of 'Lord Brahma' through extreme austerity and prolonged meditation. Pleased with the devotion of the demon, the lord blessed him with a boon that no man or Deity would be able to kill him. Empowered with the boon, Mahishasura started his reign of terror over the Earth and Heaven.
Invasion of Heaven:
People were already being killed mercilessly and even the Gods were assaulted.
Yet the worse was yet to come. It came when an strong army of demons was gathered to siege the abode of the Deities. The army was led by the king Mahishasura, the green skinned demon with the form of a giant buffalo. With its weapons of iron, and its phalanxes of elephants and charioteers the army finally marched on the king of gods, Purandara or (Indra), defeating him. Then, Mahishasura usurped the throne of heaven.

The victory was complete, and all the gods were driven out of the heaven. Routed they went to the trinity of the Supreme Gods, Brahma, Vishnu, and Shiva to save themselves and the men on the world.
The orgy of violence vis-a-vis the the invasion of the heaven by the evils enraged the Supreme Gods. Their faces were flushed with anger and a dazzling luminescence flooded forth. Great flames and thunderbolt streaked through all directions. The fires illuminated all the three worlds: the heaven, the earth, and the nether-world with penetrating beams of light.
The Birth of Durga:
At a single point, the energy of all the fires coalesced and assumed a shape, in the form of a young woman. Her face was from the light of Shiva. Her ten arms were from Lord Vishnu. Her legs were from Lord Brahma.
The dispossessed gods were awed by the supreme energy and enchanting beauty of the conceived Goddess. They praised her and equipped her with their divine gifts: Shiva gave Her a trident with a spear-end. Krishna gave her rotating disc. Varuna, the God of sea, gave her a conch and the God of fire gave her a missile. From the wind, Vayu, she received arrows. The king of gods, Indra, gave her the thunder-bolt, and the gift of his white-skinned elephant Airavata was a bell. From Yama, the god of death, Durga received a rod, and from the Ruler of Waters she was given a noose.Durga received many other precious and magical treasures-- gifts of jewels, new clothing, and a garland of immortal lotuses for her head and breasts. Heaven's architect gave her a bright axe and magic armor. God of mountains, Himalayas gave her jewels and a magnificent lion to ride into battle.Now equipped with the fearsome weaponry and magical powers of the gods, and dressed in golden armor and jewels she set off, seated gracefully upon the lion. His thunderous roars shook the three worlds. Oceans swelled up to scrape the sky and surf broke over the land. Continents were torn at their granite foundations as whole new chains of mountains rose, while older ranges crumbled, cracked, and gave way to dust in a thousand landslides. Seeing these cataclysmic ripplings in waves through all the three worlds, Mahishasura and his demon allies found their attention drawn from heaven to Earth. Though confident of their power and control in heaven, even the conquering demon host could not help being awestruck.

thats all i know'

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can u write it in a simpler form
ok but please mark it as the best answer