Who and Whom
Who is often confused with whom. Who is a subjective-case pronoun, meaning it functions as a subject in a sentence, and whom is an objective-case pronoun, meaning it functions as an object in a sentence.
If you can replace the word with he or she then use who.
Who is going to the restaurant tonight?
He is going to the restaurant tonight?
If you can replace it with him or her use whom.
She gave whom the package?
You gave the files to whom?