The W's and ¿

[Jessica]

Who Que
Who? whom? ¿quién(es)?
What? ¿cuál?; ¿qué?
When? ¿cuándo?; cuando
Where? ¿dónde?; donde
Which? Which ones(s)? ¿cuál (es)?
Why? ¿por qué? Because porque
How? ¿cómo?

How do you know when to use cuál or qué for what? What's the difference?

My brother takes Latin. He says Spanish is for stupid people (which isn't true of course). He's just wondering why in the Spanish language they have an upside down question mark (¿) and exclamation mark (¡).

[Rusty]

Who Que
Who? whom? ¿quién(es)?
What? ¿cuál?; ¿qué?
When? ¿cuándo?; cuando
Where? ¿dónde?; donde
Which? Which ones(s)? ¿cuál (es)?
Why? ¿por qué? Because porque
How? ¿cómo?

How do you know when to use cuál or qué for what? What's the difference?
Have a look at this post (http://forums.tomisimo.org/showthread.php?t=1511&highlight=cual+noun).
The interrogative pronouns above should be capitalized if they begin a sentence.

... He's just wondering why in the Spanish language they have an upside down question mark (¿) and exclamation mark (¡).

The inverted question mark and exclamation point were not originally in Spanish. The marks were suggested by the RAE in 1754, but people have been slow to adopt them. In fact, there are some Spanish speakers who still don't use them. The trend with the younger generation is to omit them, as well. This practice is frowned upon by teachers.

[Jessica]

I understand now. thanks :)

[tmember]

When do you use qué or quál for 'what'?

Edit....sorry about this, here's the perfect answer given above: Have a look at this post (http://forums.tomisimo.org/showthread.php?t=1511&highlight=cual+noun).