On the day of Shivratri,, Shiva was born- it is his birthday! Every Shivratri,, we perform sacred prayers at exactly midnight, when he was born.
Shivratri is important for women in particular. Married women pray for the good of their husbands and sons, while unmarried women pray for a great husband like Shiva.
Shivratri was also the day that Shiv and Parvati Mata got married.
Most HIndus fast and perform many auspicious penances on the day of Shivratri for health, wealth, and a spiritually content future.