"How do you cook the soup?"
Translation:Bạn nấu canh như thế nào?
Thế nào is mostly used in the North while làm sao is more prevalent in the South. You can say "Làm sao bạn nấu canh?" I suppose "như thế nào?" is normally placed at the end while "làm sao" is usually at the beginning. "như thế nào?" also means "what is ... like?" as in "Giàu có là như thế nào?" = What is it like being rich?
I am struggling with this too, the lack of any explanation is very difficult but in the end I think think the answer to your question is "yes, we do". Otherwise we will not understand when we see or hear alternative constructs. However I agree it is very painful and quite demoralising! BTW My vietnamese wife tells me that "nhu the nao" is always at the end of the sentence whereas lam sao can be used at the start.