Gallstones are small, pebble-like formations in the gallbladder, primarily consisting of hardened cholesterol and bilirubin, and they can cause symptoms if they obstruct bile ducts. Diagnosis often involves ultrasound or other imaging tests, and treatment can range from monitoring asymptomatic cases to cholecystectomy for symptomatic ones. Factors influencing gallstone formation include genetics, diet, obesity, and certain medications, with specific populations at higher risk.