Digestion can be described as a process of absorption of nutrients from food by the body and expulsion of unabsorbed waste products. It involves the breakdown of food into smaller and smaller components until they can be absorbed and assimilated.
The human digestive system comprises of the gastrointestinal tract and accessory organs of digestion such as tongue, salivary glands, pancreas, liver and gall bladder.
Digestion starts with the mechanical process of chewing. Chewing mixes food with enzyme loaded saliva. Food then can be swallowed down the esophagus into the stomach where it mixes with gastric juices. This mix is then propelled into the duodenum where it is mixed with more enzymes secreted by the pancreas.
How does is food propelled down the gastrointestinal tract? It is achieved by peristalsis of muscles. Peristalsis can be described as radial contraction and expansion of muscles in the esophagus, stomach and the rest of the gastrointestinal tract producing chime – a semi-fluid mass which when fully broken down in the small intestine is absorbed into the lymphatic system as chyle - a milky body fluid containing lymph and emulsified fat. The lymphatic system is part of the vascular system and the immune system, comprising a network of lymphatic vessels that carry lymph directionally towards the heart to mix with the blood to be circulated.
Most of the absorption and assimilation takes place in the small intestine although water and some minerals are absorbed into the blood in the large intestine. The waste products of digestion are then defecated.
Reference:
https://en.wikipedia.org/wiki/Human_digestive_system