How
The army was found when a few local farmers were trying to build/dig a new well, they were digging down and the found vault 1. There were 3 pits/vaults were all the clay sculptures were found. Vault 1 was the biggest vault, followed by vault 2 and 3. The bodies of the soldiers were made in an assembly fashion line. But the legs, arms, torsos and heads were made using moulds. Then after that custom features (such as ears, mustaches, hair and weapons) were added. The entire army was around 8,000 life-size Chinese terra cotta figures of warriors, horses and chariots.
Why
All the sculptures represent the army that triumphed overall other Chinese armies in the Warring States Period. But its original purpose was to be an afterlife army for the first Emperor Qin. It was also to accompany and protect him during his afterlife, to keep him safe even after he had passed away.