Who & Whom

when to use what?

RULE : Substitute “he/him” or “she/her”:
If it can be “he” or “she,” then it's “who”
If it can be “him” or “her,” then it's “whom”

eg.
Mrs. Dimwit consulted an astrologer whom she met in town. (She met him in Seattle.) 
    Jones is the man whom I went fishing with yesterday. (I went fishing with him.) 
    Joyce is the girl who got the job. (She got the job.) 
    Whom can we turn to in a time of crisis? (Can we turn to her?)
    Who is that masked man? (He is Tommy.)
    The men, four of whom are ill, were jailed. (object)