A hook is a curved piece of metal or other hard material that's used or pulling or holding something. A tow truck is equipped with a large hook to pull cars, and the fictional Captain Hook came equipped with an iron hook to pull off dastardly deeds.
There are coat hooks in a classroom, picture hooks on the your walls, and fishhooks for catching trout in a lake. You might have a hook and eye lock on your bedroom door, or enjoy crocheting scarves with yarn and a crochet hook. To catch a fish or a loop of yarn is to hook it. In boxing, a curving, bent-elbow punch is a hook. and in basketball a hook shot is a high, one-handed, sweeping play.