Short answers, pulled from the story.
A firearm is any type of gun that shoots projectiles using high explosive pressure generated from the combustion, or deflagration, of a chemical propellant. That propellant is most often black powder in antique firearms and smokeless powder in modern ones. The expanding high-pressure gas drives one or more projectiles down the barrel.
The first firearms originated in 10th-century Song dynasty China. Soldiers mounted bamboo tubes containing gunpowder and pellet projectiles onto spears to create the portable fire lance. It was used as a shock weapon in the siege of De'an in 1132.
The oldest surviving gun is the Heilongjiang hand cannon, a bronze hand cannon dating to 1288. It was found in the Acheng District of Heilongjiang, China. It had a 17.5 cm barrel of 2.5 cm diameter, measured 34 cm long, and weighed 3.54 kg without its wooden handle.
A handgun is a firearm that can be used with a single hand and is the smallest of all firearms, common as a sidearm or concealed carry weapon. A long gun has a notably long barrel, typically 10 to 30 inches, and is designed to be held and fired with both hands while braced against the shoulder.
The Small Arms Survey reported over one billion firearms distributed globally, of which 857 million, about 85 percent, were in civilian hands. U.S. civilians alone account for 393 million, about 46 percent of the worldwide civilian-held total. The world's armed forces control about 133 million, and law enforcement agencies about 23 million.
An assault rifle is a selective-fire rifle chambered in an intermediate cartridge such as 5.56x45mm NATO or 7.62x39mm and fed with a detachable magazine, originating with the StG 44 in World War II. A battle rifle is larger or longer and is chambered in a full-power cartridge such as 7.62x51mm NATO, examples including the M1 Garand and M14.
The earliest mechanism was the matchlock, which ignited powder with a burning cord. It was followed by the wheellock, supposedly invented by Leonardo da Vinci, then the flintlock, which struck flint against a frizzen, and finally the percussion cap or caplock, which came into wide service in the early 19th century.