It's always good to be polite - good manners can open doors especially when you've just arrived in a foreign country, you're on your own and looking to make friends...and find food! Mandarin Chinese doesn't have a specific word for 'please' but rather constructions and verbs which can be used to request things politely. However, there is a word for 'thank you' and that word is ‘谢谢’ pronounced ‘xièxie'. Note that the second 'xie' doesn't have a tone on it. Considering you've already got a falling tone on the first 'xie', it would be rather difficult to keep falling, so the second 'xie' is toneless. 谢 means 'to thank' but can also be used to mean 'to make an apology, excuse oneself'. (Examples and explanations will be added later!) Of course, there are no rules for the usage of this - thanks are always appreciated in any culture.