What is cuneiform? Why was it developed by the Sumerians? How does it differ from pictographic writing?

According to the Ancient History Encyclopedia, cuneiform was a system of writing first developed by the ancient Sumerians of Mesopotamia 3500-3000 BCE. It is considered the most significant among the many cultural contributions of the Sumerians and the greatest among those of the Sumerian city of Uruk which advanced the writing of cuneiform 3200 BCE. I can't answer the other ?. hope this helps tho.