Writing was used for record keeping to correctly count agricultural products, for keeping the calendar to plant crops at the correct time. However, writing isn't an absolute requirement of urban culture. The Incas and earlier Andean civilizations never developed a writing system. The Mississipians who built Cahokia didn't seem to have used any kind of record keeping at all, but they built very impressive cities in the American Midwest. Because writing is so intricate there has been many theories concerning the origins of writing .
Writing systems differ structure, stylistically, familially, geographically, and so on.
Alphabetical listing of scripts, just for your convenience. The study of writing systems is a very broad field, and I cannot claim that this website will reveal every detail. Far from it, in fact. There are many good books out there, and you can start in my Bibliography section.