Short answers, pulled from the story.
Leo Tolstoy wrote A Letter to a Hindu on the 14th of December 1908. He addressed it to Tarak Nath Das, who had sent Tolstoy two letters requesting support for India's independence from colonial rule.
Tolstoy spent seven months writing the letter, producing twenty-nine drafts across four hundred and thirteen manuscript pages. The finished letter ran to six thousand words.
Tolstoy argued that the Indian people could only gain independence through the principle of love, expressed as nonviolent resistance including protests and strikes. He saw the law of love as present in all the world's religions and rejected violent revolution as the alternative.
Gandhi, then living in South Africa and early in his activist career, wrote to Tolstoy in 1909 requesting permission to reprint the letter in his newspaper Indian Opinion. He then translated the letter from English into Gujarati himself. The letter, alongside Tolstoy's 1894 book The Kingdom of God Is Within You, helped shape Gandhi's views on nonviolent resistance.
The letter was first published in the Indian newspaper Free Hindustan. Gandhi later reprinted it in his South African newspaper Indian Opinion in 1909.
The Tirukkuṟaḷ is an ancient Tamil work of moral literature. Tolstoy referenced it in A Letter to a Hindu, calling it the 'Hindu Kural', and his mention introduced Gandhi to the text. Gandhi subsequently studied the Tirukkuṟaḷ while in prison.