What is dot used for Polkadot?

Could you elaborate on the functionality of the dot token in the context of Polkadot? I'm curious to understand its role in this ecosystem. Does it serve as a means of exchange? Does it confer any governance rights or staking opportunities? Also, how does it contribute to the interoperability and scalability of the Polkadot network? It seems to be a fundamental component, but I'd like a deeper understanding of its significance and usage.