FileVault is a full disc encryption program in Mac OS X 10.3 and later to protect your data and prevent unauthorized users from retrieving the information stored on your Mac. Once you encrypt your device, anyone without a password or recovery key will be unable to log in to your Mac.
There are several ways to encrypt your macOS devices.
Institutional Recovery Key
Personal Recovery Key
Institutional and Personal Recovery Key
The whole disc encryption appears seamless while you use the computer.