Who is used in reference to a "Subject", that is, someone that carries out an action Who gave the milk to the old man? Who was in the car wth you? The boys who stole the car are the ones that robbed the bank yesterday. Who received the keys to the office? Whom is used in reference to an "Object", that is, the one upon which the action was carried out To whom did you give the milk? Whom did he give the car to drive? Whom did the police catch breaking into the bank and driving the stolen car? I just saw the man to whom the office keys were given. Hope this helps.

who is the nominative。 whom is 宾格。

because i dont kow how to say 宾格 in english la ~~ 宾格 say it in english looks like bingo ..

Metane's answer can't be better. However, in spoken english it is now acceptable to use 'who' for both the subject and the object. 'Whom' can sound a little formal in informal situations. So, when talking casually you can say: 'Who gave it to you?' or 'Who did you give it to?'