Digestion begins in the mouth, when we chew and swallow, and is completed in the small intestine. Digestion involves the mixing of food, its movement through the digestive tract, and the breakdown of food into smaller molecules. The digestive process varies for different kinds of food. Go to FNIC's Diet and Disease > Digestive Diseases and Disorders for more information about the process of digestion.
Also, see NDDIC's Your Digestive System and How It Works (link is external), which explains how food is digested and why digestion is important. This resource is also available in Spanish (link is external).