Short answers, pulled from the story.
The Cultural Revolution, formally known as the Great Proletarian Cultural Revolution, was a sociopolitical movement in the People's Republic of China launched by Mao Zedong in 1966. It lasted until Mao's death on the 9th of September 1976. Its stated goal was to preserve Chinese communism by purging remnants of capitalist and traditional elements from Chinese society.
Death toll estimates vary widely. Andrew G. Walder's 2014 review of 2,213 county annals estimated 1.1 to 1.6 million deaths between 1966 and 1971. The CCP History Research Center counted 1.728 million "unnatural deaths" in its internal investigations. Estimates from other sources range from 400,000 to over 7 million. Most deaths occurred after the mass movements ended, during organized campaigns to consolidate order.
The Red Guards were cadres of mainly young students who formed in response to Mao Zedong's call in 1966 to bombard the headquarters of counterrevolution. They originated in schools and universities and later spread to factories and other institutions. Between August and November 1966, eight mass rallies drew twelve million people, most of them Red Guards. Mao formally ended their authority over the PLA on the 27th of July 1968.
The Four Olds were old ideas, old culture, old customs, and old habits. Lin Biao called for their destruction at mass rallies in 1966. Red Guards responded by burning books and historical texts, besieging the Temple of Confucius in Qufu, destroying temples, churches, mosques, and monasteries, and forcing many Tibetan Buddhists to participate in demolishing their own monasteries at gunpoint.
Lin Biao rose to become Mao's constitutionally designated successor at the 9th National Congress in April 1969, the only time any communist party had enshrined a successor in its constitution. By 1971 his relationship with Mao had broken down. According to official sources, his son Lin Liguo drafted a coup plan called the Outline for Project 571. On the 13th of September 1971, Lin, his wife Ye Qun, and Lin Liguo fled by plane and crashed in Mongolia, killing everyone on board.
The Cultural Revolution effectively ended with Mao Zedong's death on the 9th of September 1976. On the 6th of October 1976, the Central Security Bureau's Special Unit 8341 arrested all four members of the Gang of Four in a bloodless coup. The trial of the Gang ran from 1980 to 1981, with the court finding that 729,511 people had been persecuted by the Gang and 34,800 had died. In 1981, the Communist Party declared the Cultural Revolution "responsible for the most severe setback and the heaviest losses suffered by the Party, the country, and the people since the founding of the People's Republic."