What is Coinbase base?

Excuse me, I'm new to the world of cryptocurrency and finance, and I've heard a lot about Coinbase. Could you please elaborate on what Coinbase base actually is? Is it a type of cryptocurrency? Or is it a platform where people can buy, sell, and store cryptocurrencies? If it's a platform, what makes it unique compared to other similar services? Are there any fees associated with using Coinbase base? Also, how secure is it, and what measures does it take to protect its users' assets? I'd really appreciate a concise yet comprehensive explanation of Coinbase base.