The four stages of a supply chain are sourcing, manufacturing, distribution, and retail. Sourcing refers to the process of finding and acquiring raw materials and components needed for manufacturing. Manufacturing involves transforming the raw materials into finished products. Distribution involves the process of moving the finished products to the retailers or end customers. Retail is the stage where the finished products are sold to the end customers. Proper management of each stage is crucial for the smooth functioning of the supply chain, ensuring timely delivery of products to customers and maintaining customer satisfaction.