Key is not something you buy. The Key that you hear people talking about is the Private Key, which gives you full access and control over your cryptocurrency from anywhere around the world. And you only get to have a private key for your wallet when you’re making use of a decentralized wallet, and not centralized wallet like Coinbase.com.

Coinbase is a good wallet to use, and so far I think it’s a safe platform, except that they are the ones keeping your cryptocurrency for you, and you only have your email and password, but as always a lot of people are going to prefer to hold their private keys, because they know that private keys gives them the complete control over their wallet.