These styluses were essentially sharpened reeds, much like a modern-day pen or pencil. They were dipped in wet clay, and then the pointed end was pressed into the soft clay to create wedge-shaped marks, hence the name "cuneiform" (meaning "wedge-shaped").
These wedge-shaped marks represented syllables, words, and even entire concepts. The Sumerians used these clay tablets for various purposes, including record-keeping, literature, and even personal letters.