buy something for somebody意思是“为某人买某物”，例如:

Can you buy a new pen for me, Dad 爸爸，你能给我买支新钢笔吗？

What did the man buy for his father 那个男人给他父亲买了什么？

My father bought a desk for me.

My mother bought a new dress for me.

I am going to buy a book for my little brother，cause he likes reading very much.