Whips should be used as an extension of your arm to assist in training your horse. Whips can aid your horse training in two ways either as a driving aid or a physical aid. 

Using your whip for a driving aid, would be anything that involves commanding your horse to perform an action. An example of this would be asking your horse to start moving forward. 

Using your whip for a physical aid, would be anything that involves directly touching the horse with the whip. An example would be using the whip to stroke the horse. This technique is often used to teach horses to accept a human's touch.