To express questions:
Can, could, will and would are used to express requests:
Eg:Can you lend me $10?
Can I borrow your car?
Could you tell me where the train station is?
Could I have a cigarette?
Will you turn off your mobile phone, please?
Would you open the door for me?
Would you mind stepping outside for a moment?
To express advice:
Should, ought to and had better can express advice:
Eg:You should smoke less.
We‘d better leave soon.
You ought to thank her.
Ought to is less frequently used and is more formal.