Can you lend me your scissors?
But what for?作什麼用?
What are you talking to him for?
你告訴他這些做什麼?
What's all that stuff for?
這些東西是做什麼用的。
What is the cake for?
這個蛋糕是做什麼用的。
What is this for?
以下的for是和前面的動詞形成片語
What are you waiting for?
你還在等什麼?
What are you looking for?
你在找什麼?