Hi Maya! First, the title should be like　 おねがいします　と　ください　のさとはなんですか （お願いしますと下さいの差とは何ですか） In the situation, we want ask something, there is not so much difference.. しおをおねがいします。 しおをください。 おねがいします is a bit politer than ください。 Because ください sounds direct. But we don't care about so much. おねがいします is useful, we can use it as ''Can you do this?''with gesture and we can call shop empoyee at restaurant. I hope that could help you.

I'd like to know the answer to this too!