Short answers, pulled from the story.
Mahatma Gandhi was an Indian lawyer, anti-colonial nationalist and political ethicist who used nonviolent resistance to lead the campaign for India's independence from British rule. Born on the 2nd of October 1869, he later inspired civil rights and freedom movements around the world. The honorific Mahatma, Sanskrit for great-souled, was first applied to him in 1914.
Mahatma Gandhi died on the 30th of January 1948 at Birla House in Delhi, when Nathuram Godse, a militant Hindu nationalist from Pune, fired three bullets into his chest at close range. He was on his way to an interfaith prayer meeting. The trial of the conspirators began on the 27th of May 1948, and Godse and Narayan Apte were sentenced to death by hanging.
The Salt March was a Satyagraha against the British salt tax in which Gandhi and volunteers marched 388 km from Ahmedabad to Dandi in Gujarat between the 12th of March and the 6th of April 1930. The aim was to break the salt laws by making salt, watched by huge crowds. The wider campaign led Britain to imprison at least 60,000 people.
Satyagraha was Gandhi's method of nonviolent protest, which he described as appeal to, insistence on, or reliance on the Truth. He first adopted it at a mass meeting in Johannesburg on the 11th of September 1906 and first formulated it as a political principle in his 1920 Resolution on Non-cooperation. It rested on ahimsa, or nonviolence, and the idea of soul force rather than physical force.
Gandhi went to South Africa in 1893 to represent the cousin of a Muslim merchant named Dada Abdullah for a salary of £105 plus expenses, expecting a one-year commitment. He stayed 21 years after facing discrimination, including being thrown off a train at Pietermaritzburg. There he founded the Natal Indian Congress in 1894 and developed his political views and the method of Satyagraha.
Gandhi did not celebrate independence on the 15th of August 1947 because he opposed the partition of the subcontinent along religious lines and was grieved by the religious violence it unleashed. Instead he fasted and spun in Calcutta, appealing for peace, and his fasting is credited with helping stop the riots there. More than half a million people were killed as ten to twelve million migrated across the new borders.