Short answers, pulled from the story.
An alphabet is a writing system that uses a standard set of symbols called letters to more or less represent the particular sounds of a spoken language, largely corresponding to phonemes. A syllabary instead assigns symbols to spoken syllables, while a logography assigns symbols to words, morphemes, or other semantic units.
The first letters were invented in Ancient Egypt as an aid to writing hieroglyphs, using about 24 uniliteral signs. The first apparently alphabetic system, the Proto-Sinaitic script, appeared in Egyptian turquoise mines in the Sinai Peninsula around 1840 BC, apparently left by Canaanite workers, and an earlier version was found at Wadi el-Hol dating to around 1800 BC.
The Phoenician alphabet, which developed before about 1050 BC, is considered the first true alphabet and the parent script of all western alphabets. It held only about two dozen distinct letters, simple enough for traders to learn, and recorded words phonemically so it could write different languages, spreading across the Mediterranean with the Phoenicians.
The Greek alphabet was the first in which vowels had independent letterforms separate from those of consonants. The Greeks chose letters representing sounds that did not exist in Greek and used them to represent vowels, which is why some scholars call Greek the first true alphabet in the narrower sense.
Sejong the Great created the Hangul alphabet in Korea in 1443. Hangul is a featural alphabet in which the design of many letters reflects a sound's place of articulation, such as P resembling a widened mouth and L resembling the tongue pulled in, and it groups letters into equally sized syllable blocks.
These three segmental scripts differ in how they treat vowels. A true alphabet such as Latin, Cyrillic, or Korean Hangul has letters for both consonants and vowels; an abjad such as Arabic or Hebrew has letters for consonants and leaves most vowels unexpressed; and an abugida indicates vowels with diacritics added to consonants, as used for Tigrinya, Amharic, Hindi, and Thai.
A dozen Ugaritic tablets from the 14th century BC preserve the alphabet in two sequences, and both have been stable for at least 3000 years. The ABCDE order later used in Phoenician continued with minor changes into Hebrew, Greek, Armenian, Gothic, Cyrillic, and Latin, which derives from the Northwest Semitic Abgad order.