"who's" and "whose"

Two of the common words being interchanged when constructing an English sentence are "who's" and "whose". While it's easy to understand the difference of the two, many people are still confuse on how and when to use them.

So, I consulted the www again to find a clear way to explain it. According to wsu.edu,

This is one of those cases where it is important to remember that possessive pronouns never take apostrophes, even though possessive nouns do (see it’s/its). “Who’s” always and forever means only “who is,” as in “Who’s that guy with the droopy mustache?” or “who has,” as in “Who’s been eating my porridge?” “Whose” is the possessive form of “who” and is used as follows: “Whose dirty socks are these on the breakfast table?”