"Why do people wear clothes?"
Translation:लोग कपड़े क्यों पहनते हैं?
Good question. This may not be the only reason, but generally speaking, "why" is placed before the word you want to know the reason for. "People clothes why wear" asks why people wear clothes. On the other hand, "People why clothes wear" asks why people wear clothes, instead of wearing something else.
Take that with a grain of salt though because the above difference can also be expressed by changing intonation, sometimes irrespective of the word order. And then there is context.