Short answers, pulled from the story.
Writing is the act of creating a persistent, usually visual representation of language on a surface. As a structured system of communication it is also known as written language, and in rare cases it may be tactile rather than visual. Historically, written languages emerged as a way to record corresponding spoken languages.
The first example of written language can be dated to the Sumerian city of Uruk, at the end of the 4th millennium BC. Writing developed independently in a handful of locations in the Early Bronze Age, namely Mesopotamia and Ancient Egypt around 3200, Ancient China, and Mesoamerica.
Writing systems are broadly classified by the units of language their symbols represent: logographic, syllabic, and alphabetic. Phonographies represent sounds of speech through alphabets and syllabaries, while logographies represent units of meaning such as words or morphemes.
The alphabet is only known to have been invented once, by a community of Canaanite turquoise miners in the Sinai Peninsula to write West Semitic languages. This earliest form is the Proto-Sinaitic script, and the Phoenician alphabet of around 1050 BC is a direct descendant.
Written language is typically more structured and formal, and while speech and signing are transient, writing is permanent and allows planning, revision, and editing. It has higher lexical density and is predominantly declarative, with fewer imperatives, interrogatives, and exclamatives than spoken or signed language.
Marshall McLuhan argued in The Gutenberg Galaxy, published in 1962, that the printing press and the shift from oral tradition to written culture fundamentally changed human society and contributed to the rise of individualism and nationalism. He famously asserted that "the medium is the message."