When did you get here?
          A little while ago.
     When do you go to school?
          At nine o'clock.

WHERE asks about a LOCATION:

     Where is he?
          At the bank.
     Where can I find a pencil?
          On the desk.

WHY aks for a REASON:

     Why did he do that?
          Because he is silly!

WHO asks about a PERSON:

     Who is that student?
          That's Kerry.

WHOSE asks about POSSESSION:

     Whose new car is that?
          It's mine!

WHICH asks about a CHOICE:

     Which one do you like?
          The red one.
     Which class did you take?
          Grammar.