For example, many horses learn to go into a trot on voice command. Horses aren't born speaking English. But if you say the word consistently enough just before you know your horse is about to trot, the sound will become linked to the action and can eventually be used to cause the behavior. The order of training is important here. Create the behavior first, and then present the cue.
Many people train in the reverse order with often confused results.
Their inexperienced horse is working on the lunge line. It's ambling along, not paying much attention to them, and they're shouting at it to trot. Remember, we know what we intend with our words and signals, but our horse doesn't. I need to know that if I hold it out in front of him at an easy height, within seconds he'll touch it. Until I have the behavior strongly in place I won't use any verbal cues.