Examples of question words:
Who do you know?
What can you do?
Whose is that?
Which city do you prefer? Moscow or Vienna?

Using question words:
Who to ask for a person
What to ask for a thing
Whose to ask for possession
Which to choose between two

Using whom:
Whom is used when the answer is in the object.
Whom did you see yesterday?
I saw John.

This format is being used less and less.
You will encounter
Who did you see yesterday.
Whom did you see yesterday.

More examples:
Who does the presentation?
Whom does the book belong to?
Whose pen is this?
Which car do you prefer? The red one or the green one?
What did you have for breakfast?