The gallbladder is a small organ that is located near the liver, it's function is to store and concentrate bile. The liver makes the bile, that is then stored in the gallbladder. Bile's role is to help us digest foods, primarily fatty foods.
The liver makes the bile, the whole biliary system looks like a tree. The gallbladder is one branch off of that tree. The liver makes the bile, it runs down the liver branch into the gallbladder. When we eat the gallbladder squeezes and squirts the bile out that branch into the main trunk down into the small bowel where it helps us digest our food.