The human digestive system is very complex and involves a lot of organs, each with their own job. The basics are: In the mouth, the teeth cut the food into smaller chunks, and the saliva(basic) begins to break down carbohydrates In the stomach, it is highly acidic, and the organ contracts and relaxes, churning the food along with the gastric acid. It also contains enzymes which begin to break down proteins. (Making the food smaller is really important as smaller things have a larger surface area to volume ratio, so enzymes can access a larger amount of it at any one time) The small intestine contains a lot of enzymes(made in the pancreas) and digestive juices such as bile (made in the liver), and is where much of the digestion (releasing the useful nutrients from the food) occurs. It is also where much of the nutrients are absorbed into the blood stream (villi give it a very high surface area). The large intestine is where water and minerals/salts are absorbed, and where feces begin to be made. I hope this helps!