In ancient times the "sling and stone" was sort of like a loaded weapon, and quite a valuable weapon if one had the skill to use it. The sling itself was usually made of wool, twined together, though some cultures used leather. In the middle there was a thick pouch (like a plaited thong) for holding and slinging the stone. The stones could be kept in a small pouch for rapid fire slinging. The user would place the stone in the pouch, hold both ends, waive it around the head, and fling it by letting go of one of the ropes.
In the Bible "slingers" were part of the Israelite army like the archers.
"And it came to pass, when the Philistine arose, and came, and drew nigh to meet David, that David hastened, and ran toward the army to meet the Philistine. And David put his hand in his bag, and took thence a stone, and slang it, and smote the Philistine in his forehead, that the stone sunk into his forehead; and he fell upon his face to the earth. So David prevailed over the Philistine with a sling and with a stone, and smote the Philistine, and slew him."
1 Samuel 17:48-50
"And they beat down the cities, and on every good piece of land cast every man his stone, and filled it; and they stopped all the wells of water, and felled all the good trees: only in Kirharaseth left they the stones thereof; howbeit the slingers went about it, and smote it."
2 Kings 3:25
Among all this people there were seven hundred chosen men lefthanded; every one could sling stones at an hair breadth, and not miss.
For thus saith the LORD, Behold, I will sling out the inhabitants of the land at this once, and will distress them, that they may find it so.