Gall stones are hard stones which form in the gall bladder. The gall bladder is a small pouch which sits on the liver. The function of the gall bladder is to concentrate bile, a digestive enzyme used in the gut to help break down fats.
Pain occurs when these gall stones become blocked in the bile ducts. The gall bladder contracts to try and force bile into the gut. However, the bile cannot pass the gall stone hence this contraction causes pain. Contraction of the gall bladder is stimulated by eating, especially when you are eating a fatty meal. Hence eating can stimulate abdominal pain from gall stones.
The abdominal pain from gall stones is typically in the upper right quadrant. Occasionally the pain may also occur in the tip of the shoulder blade, this is a phenomenon known as referred pain.