Short answers, pulled from the story.
Humans have used flint to make stone tools for more than three million years. Flint's extreme durability has made it possible to accurately date its use across this immense span. It is one of the primary materials used to define the Stone Age.
Grime's Graves in England was an important source of flint traded across Europe. In North America, Native Americans quarried flint from hundreds of sites along Flint Ridge in Ohio, and that Ohio flint has been found as far west as the Rocky Mountains and as far south as around the Gulf of Mexico.
A flint edge shaves off a tiny particle of steel, exposing iron that reacts with oxygen in the atmosphere. This reaction produces a spark capable of igniting the right tinder or gunpowder. Before steel was common, rocks of pyrite were used alongside flint for the same purpose.
The flintlock is a firing mechanism in which a spring-loaded flint strikes a steel plate called a frizzen, creating sparks that ignite priming powder and then the main propellant charge. Military use of the flintlock declined after the adoption of the percussion cap from the 1840s onward, though flintlock rifles and shotguns remain in use among recreational shooters.
The earliest known evidence of deliberately heat-treated chert comes from Hoedjiespunt 1 in South Africa. This site dates to MIS-5e, a period spanning 130-119 thousand years ago, placing the technique within the Middle Stone Age.
Flint, knapped or unworked, was used to build stone walls using lime mortar, often combined with other stone or brick rubble. It was most common in parts of southern England lacking good building stone, particularly East Anglia and chalky areas through Hampshire, Sussex, Surrey, Kent, and Somerset. Framlingham Castle is one prominent example of a large structure built with flint.