Ich sehe “Warum” und “Wieso” used as “why” and I’m wondering when I should use which one.
They mean both the same thing, and they are really interchangeable. There is even a third one which can also be used: "Weshalb" They all are translated into "why".
Warum baust du ein Haus? = Wieso baust du ein Haus? = Weshalb baust du ein Haus? = Why do you build a house?
And a fourth: Weswegen baust du ein Haus?
Warum, wieso, weshalb, weswegen: The four whys.
You can use these words synonymously. "Wieso" sounds more colloquial, whereas "Warum" can also be used in a more formal context. "Weshalb" is another synonym, which is even more formal. You can't go wrong with "Warum", it is always appropriate.
You can use "warum" at all times. "Wieso" is acceptable too. It's like the difference between "why" and "how come".
Thanks everyone! Glad this wasn’t as confusing as prepositions.