The digestive system is a one-way system. Food enters the mouth, gets digested, and wastes exit the body via the anus. The mouth is the start of the digestive system, and it does both mechanical and chemical digestion. The teeth mechanically crush, grind, tear, and rip the food into smaller and smaller pieces. The saliva moistens the food and chemically begins to breakdown sugars because saliva contains the enzyme amylase.
Once swallowed, the food moves down the esophagus which uses peristalsis to propel the food into the stomach. The food will pass through the cardiac sphincter and drop into the stomach where pepsin begins breaking down proteins along with hydrochloric acid. Food will remain in the stomach for about 3 to 4 hours. After that it will move into the small intestine where a bunch of enzymes go to work. One such enzyme is lipase which chemically breaks down lipids. Bile also helps out with chemical digestion as well. Bile is produced in the liver and stored in the gallbladder.
The first section of the small intestine is the duodenum, and most of the chemical digestion occurs here. The following two sections are the ilium and jejunum. They are covered in tiny folds called villi, and that is where the digested food is absorbed into the bloodstream to be transported around the rest of the body. Remaining materials move into the large intestine where water is absorbed. Whatever is left after that will then pass through the rectum and anus.