“Who” is a subject pronoun like “he,” “she” and “we.” We use “who” to ask which person does an action or which person is a certain way.
??Who made the birthday cake?
??Who is in the kitchen?
??Who is going to do the dishes?
“Whom” is an object pronoun like “him,” “her” and “us.” We use “whom” to ask which person receives an action.
??Whom are you going to invite?
??Whom did he blame for the accident?
??Whom did he hire to do the job?
“Whose” is a possessive pronoun like “his,” “her” and “our.” We use “whose” to find out which person something belongs to.
??Whose camera is this?
??Whose dog is barking outside?
??Whose cell phone keeps ringing?