Devi Durga was jointly created by the holy trinity - Brahma (the creator), Vishnu (the preserver) and Shiva (the destroyer) to eliminate a demon named Mahishasur, who's treachery ruined peace and sanctity in the three worlds.
Known as the destroyer of evil and enforcer of good sense and morality, Durga, the ten-armed Goddess is worshipped during Navratri, a festival spread over nine days during four different times of the year.
Out of the four Navratris, the Chaitra and the Sharadiya are the most popular. The others are Aashada and Magha Gupta Navratri.
Durga, who represents the feminine form, is worshipped during Navratri - Nav meaning nine and Ratri meaning nights.
Dressed in white, Maa Brahmacharini is the unmarried form of Sati, King Daksha’s daughter, who was later married to Lord Shiva. She is depicted holding a Japa Mala in the right hand and a Kamandala in the left hand.
Since she is governed by Mangal, the controller of all fortunes, her devotees worship her on the second day of Navaratri to seek her blessings for peace and virtue and prosperity.
You can chant this Mantra to pay ode to Goddess Brahmacharini:
देवी प्रसीदतु मयि ब्रह्मचारिण्यनुत्तमा॥
Dadhana Karpadma abhyamaksh Mala kamandalu
Devi Prasidatu Mayi Brahmacharinya Nuttam