As Fiona said. The reins are the straps (like ropes) from the bridle to the person riding the horse. A "bit" is the horizontal metal inside the horse's mouth, which is pulled left or right and touches the horse's lips.

I got it. Thanks a lot Fiona

A bridle is the headgear used to control the horse. The reins are attached to the bridle and are used by the rider to control the horse's movements.