Thief
Rogue Theologian
You are asking questions that can not be summed up in short sentences.
To understand how writing came into being, you will need an understanding of psychology, sociology, linguistics etc.
I think first you could read the following wiki article.
Writing - Wikipedia, the free encyclopedia
It explains the different ways the written word has been created and is expressed.
If you have any questions about anything you read there, i will do my best to answer it for you.
I think it started with a muddy hand print on the wall.
Taking notice it turned into a game.....
Then it turned into story telling.
Short enough?