‘Who’ denotes the subject and ‘whom’ is used for the object?

who: It’s the subject of a verb—e.g., Who gave you that book?
It’s a predicate nominative (a noun in the predicate that renames or refers to the sentence’s
subject)—e.g.,This is who I am.

Whom is an objective pronoun, which is a pronoun that receives the action of a verb. It also has
two main uses:
It is the object of a verb—e.g., Whom should I call?
It is the object of a preposition—e.g., From whom did you get this information?