Here's how you can turn on FileVault to encrypt your Mac's hard disk and protect your data from prying eyes.
1. Go to System Preferences.
2. Go to Security & Privacy.
3. Click the FileVault tab.
4. Click the Turn On FileVault button (you might need to click the lock in the bottom left corner and type in your password in order to click the FileVault button).
Please note that you will be provided with a recovery key in case you lose your password. Be sure to keep your recovery key in a safe place in case you need it later.
Additional resources for FileVault