A supply chain is a network of facilities and distribution options that performs the functions of procurement of materials; transformation of these material into intermediate and finished products; and distribution of these finished products to customers. (Source: Ganeshan & Harrison - Introduction to Supply Chain Management)

A supply chain essentially has three main parts, the supply, manufacturing and distribution:

• The supply side concentrates on how, where from and when raw materials are procured and supplied to manufacturing.
• Manufacturing converts these raw materials to finished products and
• Distribution ensures that these finished products reach the final customers through a network of distributors, warehouses and retailers.

The chain can be said to start with the suppliers of your suppliers and ends with the customers of your customer.