The Jiangmen Underground Neutrino Observatory (JUNO), located 700 meters underground in Guangdong Province, South China, has officially commenced operation following the completion of filling its liquid scintillator detector with 20,000 tons of liquid. After more than a decade of preparation and construction, JUNO has become the world's largest and first operational ultra-large-scale scientific facility dedicated to neutrino research. The observatory features a 12-storey-high transparent spherical detector made of steel and plexiglass, designed to achieve unprecedented precision in neutrino measurements. JUNO aims to determine the ordering of neutrino masses and advance the understanding of these elusive particles, often referred to as "ghost particles." The facility's data collection marks a significant milestone in the global scientific effort to explore neutrino properties.