Short answers, pulled from the story.
The Qin dynasty lasted 14 years, from 221 BC to 206 BC, making it the shortest-lived major dynasty in Chinese history. It had only two emperors, Qin Shi Huang and his successor Qin Er Shi, before collapsing after internal conspiracy and popular revolt.
Qin Shi Huang was born Ying Zheng and came to the Qin throne at age nine. Beginning in 230 BC, he led military campaigns that conquered each of the six rival states, completing the unification of China in 221 BC. He then combined the titles of the earlier Three Sovereigns and Five Emperors into the new title Shi Huangdi, meaning 'First Emperor'.
Shang Yang introduced military and administrative reforms between 359 BC and his execution in 338 BC. These included maximising agricultural land by clearing forests in the Yellow River valley, establishing a population registration system thought to date to 375 BC, and building the Qin capital at Xianyang. His reforms created the stable economy and large army that powered Qin's later conquests.
Qin Shi Huang died in 210 BC while seeking an elixir of immortality. Chief eunuch Zhao Gao and prime minister Li Si concealed his death, forged orders for the intended heir Fusu to commit suicide, and installed Fusu's younger brother Huhai as Qin Er Shi. Qin Er Shi's inept and brutal reign sparked widespread revolt; Li Si was executed, Zhao Gao engineered the emperor's forced suicide, and the final ruler Ziying surrendered to Liu Bang in 207 BC before being executed by Xiang Yu.
The Qin connected and reinforced existing border walls to form the foundation of what became the Great Wall of China. They also built a large national road system, a canal off the Wei River completed in 246 BC, and the city-sized Mausoleum of Qin Shi Huang guarded by the Terracotta Army, which remained undiscovered underground until 1974.
Qin is the most widely cited origin for the name China and its European equivalents. The term appears in Sanskrit as Cina and Sina, then entered Greek as Thinai or Sinai, and spread through European languages as China in English and Chine in French. Some scholars dispute this, noting that Sina appears in Sanskrit before the Qin dynasty's founding; alternative proposed origins include the Zhou-era state of Jin and Jing, another name for the state of Chu.