practice with 위해

My dad cooked me dinner/cooked dinner for me.
1. 우리 아빠는 나를 위해서 점심을 요리했어요.

*저희 아빠 (formal)

Since it's my friends birthday, I am going to the bookstore to buy her a book.
2. 우리 친구 생일이라서 나는 친구를 위해서 책을 사러 서점에 가고 있어요

*its more common to say just 친구 or 내 친구 when you say this kind of sentence (informal)

would be better with 제 친구 if you make it formally  :)