What is Coinbase & how does it work?

Could you elaborate on Coinbase, a leading cryptocurrency exchange platform? How does it function, and what makes it unique in the world of digital currencies? What services does it offer to its users, and how secure is it? I'm curious to understand the role Coinbase plays in facilitating transactions between buyers and sellers of cryptocurrencies, as well as the processes it employs to ensure the safety and reliability of its platform. Additionally, how does Coinbase handle the storage and custody of digital assets, and what measures does it take to protect its users' funds?