They have the same meaning and use, but the 'could' form is a little more tentative, and therefore a little more formal. You might choose to use 'could' rather than 'can' to be more polite, or to ask for a slightly bigger favour. It's similar to the difference between 'will' and 'would' in requests. The '..ould' form has a distancing effect.

Yes, SuKi has said it: more formal perhaps, a little more polite. If someone wanted a REALLY big favour from me they would be better to start it, "Could you...." And if it were a REALLY ENORMOUS sort of favour they had better throw in a 'possibly' too! "Could you possibly....... ?"

"could you" is more polite or slight accent

@Richard，thank you very much????

赵微微, Su.Ki. and MoiraWendy are correct, but "can" sometimes means "do you have the ability to do something" and "could" sometimes means "is it possible that you may be able to do something in the future (and the sentence usually includes some conditions that would make it possible or impossible". For example: Q - Richard, can you play the piano? A - No, I cannot, because I never took any lessons....... / Q - Richard, could you play the piano? A - Yes, but only if I took lessons first. Is my comment 'clear as mud'?