The gallbladder is situated under the left upper quadrant of the liver in the abdominal cavity. The chief function is to store bile that was synthesized in the liver. Bile is necessary to help emulsify and digest fats. When you eat a meal that has a high fat (lipid) content bile is secreted through the cystic duct and common bile duct into the duodenum (first part of the small intestine, small bowel). Enzymes like CCK (cholecystokinin) help the gallbladder to contract and release its contents. In the duodenum bile breaks apart the lipid chain molecules which assists in the digestion of those fats.
People with gallbladder disease have to have it surgically removed, a procedure called a cholecystectomy. This can be done laproscopically or through open laparotomy.