When do you use who and whom and what are the definitions of both?

Answer 1

The words 'who' and 'whom' are both pronouns denoting persons.
'Who' is subjective. You use it when the person in question is performing the verb.
'Whom' is objective. You use it when the person in question is receiving the verb or is the object of a preposition.

Who made the pie? (Who made... person performing action)
For whom did you make it? (For whom... person as obj. of prep.)
Who will deliver it? (Who will deliver... person performing action)
You already asked whom to take it? (...asked whom... person receiving action)

Answer 2

First of all they are Relative Pronouns. As you know, a pronoun stands in place of a noun, so if the noun is the subject of the sentence, use who. if it is the object, use whom.
eg. "Who said that? " "The person to whom I was speaking."
"The girl who gave me a kiss." The boy whom I kissed"
Hope this helps.

Answer 3

whom is when u are adressing a group of ppl for 1 person and who is when u are addressing one person.