Kahhong, give me that book.
This sounds a bit sharp because I don't know you.
Kahhong, would you give me that book.
Much politer- I don't know you, so I can't give orders.
If you want to ask a strnager to do something, then you will naturally try to show that you are polite because it's not the same as talking to a brother or sister or a friend. In English, we don't have a polite form of the word 'you', which many languages do, so we change the verbs to be polite. Once I get to know you, I can use other forms.