Please clear my confusion.What is the difference between RMB and CNY?
Thank you

Without knowing what subject you are referring to it is difficult. If airport codes, RMB is Buraimi, Oman and CNY is Moab, Utah, USA.

CNY is Chinese Yuan
RMB is Ren Min Bi. literally, the people's currency.

Both are correct. Yuan refers to the unit of currency and RMB refers to the time when there was a dual currency here, also the FEC, Foreign exchange certificate. (The currency, RMB, is still not freely convertable)

In spoken Chinese, people will say that something costs 10 yuan or more likely 10 KUAI. (Kuai is like saying bucks instead of dollars). In writing, Yuan is used, but in spoken almost always KUAI.

You won't see CNY unless pricing online or at the bank.

CNY means Chinese New Year to me and most people in Asia. Yuan is always Yuan. (Pronounced Won.)

Yuan is not always yuan, it is called kuai in spoken Mandarin and it is certainly not pronounced won in Mandarin. It is pronounced Yoo-won.

Bchen is correct, the spoken version in China is almost always kuai (even in Taiwan where a different currency exists, you'd still refer to it as kuai if you're a Mandarin speaker). CNY and RMB both refer to the currency of mainland China with CNY the designation used by currency traders. I don't know where yuan would be pronounced 'won' either.

"Kuai" means piece. For "10 bucks", one's supposed to say something like "shi kuai qian", which means "10 piece money". But people just say "shi kuai" in short.

In Cantonese, there are even more ways to say "10 bucks". "Sup mun", "Sup pei", and if there are cents after, we say "Sup gor" something... What you'll never hear people say is "Sup yuan", though that's how it's written.