How can I make a polite request using : would you..? Could you...? Can you...? And will you..?
Here are some examples:
1. Would you answer my question, please? - polite.
2. Could you help me with my cases, please? - polite.
3. Can you hold this for a moment, please? - slightly less polite than "could". For instance, if you were were asking a close friend or relation to do something, you could use "can you" and omit "please".
4. Will you take this letter to the postbox for me, please? - slightly less polite than "would".
You could say that "could" and "would" make the request more "remote", and so more polite.