Hello Mike, The ancient Chinese people had a strong belief in the afterlife and saw death as a continuation of their present life. The Army was built and buried in front of the Emperor Qinshihuang's tomb ,the first emperor (r. 221-207 BC) to defend him in the afterlife, protect his tomb and to boast his power and show loyalty to him after his death.

In the past (well..., in the past past, over a thousand years before Qin Dynasty we're talking about) there was the custom that deceased (/dead) kings were accompanied by concubines, courtiers and sacrificed slaves (/prisoners of war) in their tombs. Ages after that the first Qin emperor made enormous changes in society as well as in funeral rites. The army was the main pillar of his power. So their effigies had to protect him in death. We always talk about the Terracotta Army. At Lintong there is a whole palace, with double walls, gates, offices, stables and everything the emperor had in life. The army is only a small (the outer and best known) part of those installations. Later, in Han Dynasty there were some imperial tombs with a large number of figurines. But of smaller size.

The emperor of ancient Chinese believes that he is to another world where he also want to be a emperor after he died.Therefore the Terracotta Army which to be considered as a really Army prepared to help emperor conquer the world he is going to live in after he died was built.Up to now,lot of Terracotta Army haven't been discovered. (I guess these)

mummies are/were not builded. Everything can be explained but not in few lines. you better look for a book on ancient chinese history and culture to get a general idea.

why Egyptians built mummies?