The greatness of Amalaki Ekadashi was narrated by Sage Valmiki. It is a celebration of the amalaka or amla tree, known as the Indian gooseberry. It is believed that by observing Amalaki Ekadasi, a devotee attains Moksha and washes away all the sins committed. Special pujas and offerings are made to the Amalaki Tree on this day.
Shiva (Lord Shiva) + ratri (night), so Shivaratri means the night of #LordShiva. Devotees of Krishna view Lord Shiva as the greatest Vaishnava. Therefore, Vaishnavas celebrate by seeking Lord Shiva's blessings and worship him.