What is OKCoin & how does it work?

Sure, here's a description simulating a questioner's tone with a word count of no more than 300: "Hey there, I've been hearing a lot about this platform called OKCoin, but I'm not entirely sure what it is or how it works. Can you fill me in? Is it some kind of exchange where I can buy and sell cryptocurrencies like Bitcoin and Ethereum? How does it differ from other exchanges out there? And what kind of security measures does it have in place to protect users' funds? I'd love to learn more about this platform and see if it's a good fit for me.