How did the Sumerians invent writing

They used wedged-shaped symbols in a kind of writing called cuneiform

Sumerians lived in the Fertile Crescent area of modern Iraq. After the invention of agriculture, they made tablets from the nearby river mud. While these clay tablets were still wet, they used a sharpened stick, called a stylus to make markings on the tablet to keep records of sales and purchases of grain. Believe it or not, his wedge-shaped style of writing, called cuneiform, was invented by ancient accountants.