"Was für" is not "what for"

Although the German words was für may translate directly as "what for" as separate words, when you put them together they have a different meaning. If somebody asks you to do something in German and you want to know "What for?", you would properly respond with "Warum?" ("why") or "Wofür?", which is another way of saying "why."

In English, the word combination was für usually means "what" or "what kind":

Was für ein Geschenk soll ich dir mitbringen?

What kind of present should I bring [back] with me for you?

Caption 14, Märchen - Sagenhaft - Die Schöne und das Biest
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Hach Gott, was für ein Tag!

Oh god, what a day!

Caption 8, Kein Kredit - im Land der Klone
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The phrase was für in other contexts can also mean "something for":

Also, wär' der Modeljob definitiv was für dich?

So, would the modelling job definitely be something for you?

Caption 10, RNZ Top Model - Casting 2010
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In the example above, the word was is functioning as a shortened version of etwas, which means "something."

Further Learning
Go to Yabla German and put in the search words "what kind" to see the different ways that was für is used in different contexts.