BNB is the digital token of Binance.
It is mainly used to pay trading fees, use services on the platform, and support different blockchain activities.

BTC (Bitcoin) is the first and most well-known cryptocurrency in the world.
It is mainly used as a digital store of value and for sending money without banks.

In short, BNB is mostly used inside the Binance ecosystem, while BTC is used globally as a digital currency and investment.