What was young David doing when Samuel came to anoint one of Jesse's sons?

Answer: Tending the sheep

Jesse said, "There is still the youngest, but he is tending the sheep." Samuel sent for David and anointed him.

“And Samuel asked him, “Are these all the sons you have?” “There is still the youngest,” Jesse replied, “but he is tending the sheep.” “Send for him,” Samuel replied. “For we will not sit down to eat until he arrives.””— 1 Samuel 16:11 (BSB)