Short answers, pulled from the story.
The Congo Crisis was a period of civil war, secessionist conflict, and Cold War proxy intervention in the Republic of the Congo lasting from 1960 to 1965. It began almost immediately after the country gained independence from Belgium on the 30th of June 1960 and ended with Joseph-Desire Mobutu's second coup on the 25th of November 1965. Around 100,000 people are believed to have been killed.
Patrice Lumumba was the prime minister of the newly independent Republic of the Congo and the leading figure of the Mouvement National Congolais (MNC). He was captured on the 1st of December 1960 after fleeing house arrest, and on the 17th of January 1961 he was executed by Katangese troops near Elisabethville with assistance from Belgian officers and personnel.
Moise Tshombe declared Katanga independent on the 11th of July 1960, motivated by a desire to keep the province's mining revenues rather than share them with the rest of the Congo, and by what CONAKAT called the disintegration of law and order in the north and east. The Union Miniere du Haut Katanga (UMHK), fearing nationalisation, backed the secession financially, and Belgium provided direct military support. The secession ended on the 17th of January 1963 when Tshombe surrendered his final stronghold at Kolwezi.
The Congo Crisis was also a Cold War proxy conflict. The Soviet Union sent around 1,000 military advisers to support Lumumba, and later supplied the Simba rebels. The United States backed Kasa-Vubu, supported Mobutu's coup, provided aircraft for the Belgian intervention in Operation Dragon Rouge in November 1964, and the CIA materially supported the mercenary unit 5 Commando ANC.
The Simbas were Maoist-inspired Congolese rebels who rose up in 1964 calling for a "second independence" from kleptocracy. The name came from the Kiswahili word for "lion." They believed that by following a moral code they could become invulnerable to bullets, made use of magic and witchcraft, and founded the People's Republic of the Congo in Stanleyville with Christophe Gbenye as president.
The crisis destabilised Central Africa and helped ignite the Portuguese Colonial War, particularly Angola, where the União dos Povos de Angola launched the Baixa de Cassanje revolt in 1961, starting a conflict that lasted until 1974. It divided newly independent African states into moderate and radical blocs. In Chad, the FROLINAT rebellion of 1965-1979 explicitly rejected secessionism in direct response to the Katanga example, declaring "there will be no Katanga in Chad." The chaos also influenced white-minority governments in Southern Rhodesia, which declared independence unilaterally in 1965.