'see' is the instinctive action bestowed upon you as a naturally given faculty ,that of sight. 'look' is a voluntary action, where you direct this faculty towards a person or a thing,that is why you mostly use the preposition 'at' after it ( look at ). It is willingly catching a brief sight of a visible entity. 'look at' could aslo mean to examine something thoroughly ,but that is not the meaning comparable with 'see' here. Example: "She turned to look at him and saw instead a beautiful girl in front of her." The voluntary action was 'to look' at someone ,but what the eyes caught 'saw' was a girl . 'watch' is the action of a continuous direction of sight towards an event, show or anything performed in the range of your vision ( to watch a movie, show, performance,sport event etc..)