Short answers, pulled from the story.
A crank is an arm attached at a right angle to a rotating shaft. When combined with a connecting rod, it converts circular motion into reciprocating (back-and-forth) motion, or the reverse. Almost all reciprocating engines use cranks and connecting rods to transform piston motion into rotational motion.
Pottery models of crank-operated winnowing fans from the Western Han dynasty, dating back to 202 BC to 9 AD, are among the earliest confirmed examples. Rotary querns with crank-like handles appeared in Spain between 600 BC and 500 BC. The Antikythera mechanism, dated to around 200 BC, also incorporated a crank.
Roman-era sawmills at Hierapolis in Asia (3rd century AD), Gerasa in Syria, and Ephesus in Ionia (both 6th century AD) used crank-and-connecting-rod systems to power stone-cutting frame saws. A Roman iron crank of unknown purpose, 82.5 cm long, was excavated at Augusta Raurica, Switzerland, and dated to the 2nd century AD.
Al-Jazari (1136-1206) described crank-and-connecting-rod systems in water-raising machines and incorporated a crankshaft into his twin-cylinder pump. The German military engineer Konrad Kyeser documented crank uses in Bellifortis in the early 15th century. Roberto Valturio designed a multi-crank paddle boat in 1463, and Agostino Ramelli's 1588 work depicted eighteen examples of cranks integrated into machine design.
The Citroen 2CV, produced from 1948 to 1990, was the last car model to incorporate a hand crank as standard equipment. Before electric starters became common, nearly all early 20th century automobiles required hand cranks, called starting handles in the United Kingdom.
The Utrecht Psalter, dated around 830 AD, contains the earliest known depiction of a crank-operated rotary grindstone. Compound cranks appeared in depictions of the carpenter's brace between 1420 and 1430. By the early 15th century the crank was common across Europe, with its spread documented by engineers such as Konrad Kyeser and the anonymous writer known as the Anonymous of the Hussite Wars.