Significance
Sharad Navratri is the most important of the year's Navratris — nine nights devoted to Goddess Durga in her nine forms (Navadurga), celebrating the triumph of the divine feminine (Shakti) over the demon Mahishasura.
It culminates in Vijayadashami (Dussehra), the day of victory.
Rituals
The festival begins with Ghatasthapana (Kalash sthapana) and the sowing of barley. Each day a different form of Durga is worshipped, many devotees fast, and evenings resound with Garba and Dandiya. Kanya Pujan (worship of young girls) is performed on Ashtami/Navami.
How the date is fixed
Sharad Navratri begins on the Pratipada of Ashwina Shukla paksha and runs nine days; the Ghatasthapana muhurat is set at the start of the first tithi for your location.