* Whose is the possessive form of "who," meaning "belonging to whom."
* Who's is a contraction of "who is" or "who has."
Here are some examples:
* Whose book is this? (meaning "belonging to whom")
* Who's coming to the party? (meaning "who is coming")
* Whose turn is it to go? (meaning "belonging to whom")
* Who's been eating my cookies? (meaning "who has been eating")