Emotion is a reaction to one's thoughts about something. For example, you might be emotionally moved when someone insults you. This would be a negative reaction. By that I mean, it would result in an unpleasant feeling in the body (not generally felt by most, as they react)
On the other hand, it could be an entirely different type of emotion, one of great sadness when a puppy dies in one's arms. Once again, this is a feeling that comes up for two reasons, sadness for the animal, and sadness for oneself at the loss of perhaps a canine friend.
The body can trigger emotion: the mind can trigger emotion. Clench your fists and scowl and you can make yourself angry. Sit up straight when slouching and you can become alert and feel good about yourself. Emotion is something we all need to be very aware of, or it will rule our lives.