Who - refers to a person

ex. Who are you ?
Who is that girl ?

Whose - refers to a stuff/thing belonging to a person .

ex. Whose ballpen is this ?
Whose wallet is this ?

Which - What, of those mentioned or impliedĀ .

ex. Which one is bigger ?
Which one is better ?

Whom - What person or people; which person or people, as the object of a verb.

ex. Whom did you ask ?
To whom it may corncern.

That - an object/person that you are pointing to ; an object or person far from you .

ex. What is that ?
Is that Jenny ?