In this form Durga is seated on a lotus and is four armed. She holds a lotus, mace, discus and book.
In this form Durga removes ignorance and she provides the knowledge to realize That or Brahman. She is surrounded by Siddhas, Gandharvas, Yakshas, Demons and Gods who are worshipping her.
The Siddhi that she provides is the realization that only She exists. Siddhidayini form of Durga is worshipped on the ninth day of Navaratri.
She is the mistress of all achievements and perfections. The narrative regarding her emergence runs as follows:
When the Universal Mother was gripped with the idea of projecting Creation, She, first of all, created Lord Shiva who prayed to Her to endow him with perfections.
For this purpose, the Universal Mother (Durgaa) produced Goddess Siddhidaatri from Her own person.
As the behest of the Universal Mother, Goddess Siddidaatri bestowed eighteen kinds of rare perfections and powers and potentialities (Siddhis) on Lord Shiva.
By virtue of these siddhis, Lord Shiva happened to develop a divine splendor.
Having acquired the siddhis from Goddess Siddhidaatri, Lord Shiva created Lord Vishnu who in turn created Lord Brahma who was entrusted with the task of the Creation whereas Lord Vishnu got the task of Protection and Lord Shiva that of Destruction.
Lord Brahma felt a great difficulty in his task of the Creation in the absence of man and woman.
Thereupon he remembered Mother Siddhidaatri.
When she appeared before him, Lord Brahma said to her, “Oh Great Mother! I cannot carry on with the task of the Creation in the absence of man and woman. You kindly solve this problem of mine through your supernatural attainments (siddhis).”
Having heard Lord Brahma, Mother Siddidaatri converted half the person of Lord Shiva into a woman.
Thus Lord Shiva became half-male and half-female and came to be known as Ardhanaarishwara.
Thus the problem of Lord Brahma was resolved and the task of the Creation went on smoothly.
Mother Siddhidaatri possesses four arms and she rides on a lion. She carries the mace, the lotus, the conch-shell and the disc in her four hands. He who acquires her grace attains salvation after enjoying the pleasures of life. She fulfills all the mundane and divine aspirations of her devotees. Her worship destroys all distresses.