FileVault offers the fantastic option in macOS to encrypt your entire drive. With modern Macs, starting now several years ago, that whole-disk encryption allows nearly the same performance as with an unencrypted drive due to hardware-based accelerated cryptographic calculations.
To avoid losing your files forever if you forget your password or lose it from a stored location, macOS offers to either reveal to you a special Recovery Key that you have to make a record of, or—starting with Yosemite—lets you use iCloud to unlock your drive. (There’s a special Mavericks-only option that requires answering security questions; read this Apple support note for details, especially the footnote at the end.)
