Coinbase is a digital currency exchange headquartered in San Francisco, California. They broker exchanges of Bitcoin, Bitcoin Cash, Ethereum, Ethereum Classic, Litecoin, Tezos, and many others, with fiat currencies in 32 countries, and bitcoin transactions and storage in 190 countries worldwide.
Authy is a two-factor authentication app that Coinbase endorses as a way to help keep your account more secure. Two-factor authentication is an extra layer of security that requires you to use something you know (like your password) and something you have (like your phone) to log in.
Authy generates unique one-time passcodes that you use in addition to your password when logging in.
Coinbase has been known to be one of the most secure exchanges in operation today. In addition to 2FA via Authy, they offer a host of other security features like U2F hardware keys, multisig vaults, and insurance.