An atomic bomb uses nuclear fission (splitting atoms like uranium or plutonium) to release immense energy as heat, blast, and radiation, causing massive destruction, as seen in Hiroshima and Nagasaki during WWII, resulting in widespread death, fires, and long-term radiation sickness from severe burns and cancers. The two bombs dropped, "Little Boy" (uranium) and "Fat Man" (plutonium), unleashed power equivalent to thousands of tons of TNT, with devastating effects on people, buildings, and infrastructure.