Shivrati marks the darkest night of the year where God is worshiped in the form of Shiva the Destroyer. Many Hindus fast throughout the day, chant mantras and the holy names of God, sing devotional songs, and bathe and make offerings to Shivalingam. The actual moment of Shivratri is usually around midnight, marking the darkest night of the year.

To observe the holiday also has symbolic significance – devotees worship at night to remove any spiritual darkness in their life and to increase their devotion.

Read more:
Shivratri by Swami Sivananda
Significance of Shivratri

Related links:
Muslim donates land for construction of Shiva temple
Kashmir Hindus & Muslims reunite for Shivratri