look是强调看的动作.例：look!it is a bird.
see是强调看的结果,强调的看得见看不见.例：i can see a bird.
watch用在看电视看比赛的时候.例：let's watch tv together.
look at是look的短语,look本身是不及物动词,如果它要带宾语的话,后面就必须要有一个介词,所以有look at这个短语,意思是看着某某.例：look at the blackboard,everyone.