With FileVault 2 you can encrypt the contents of your entire drive to help keep your data secure. FileVault 2 uses full disk, XTS-AES 128 encryption to help keep your data secure. Using FileVault 2, you can encrypt the contents of your entire drive.
System Preferences > Security & Privacy > FileVault tab (click the lock to make changes if necessary)
Choose your recovery method.
Restart your computer.