You can encrypt your Mac hard drive OR create an encrypted area of your drive. 

Encrypting your Macintosh hard drive OS 10.8 or above

1. Go to System Preferences.

2.  Click Security & Privacy.

3.  Click the FileVault tab.

4.  Click “Turn on FileVault”

5.  If your computer has multiple user accounts, a dialogue box will drop down asking you to confirm user accounts that are allowed to unlock the encrypted drive.

6.  Enable any necessary users and click Continue.

7.  Another dialogue box will drop down asking you to copy the recovery key, which is an alternative to unlocking your disk if you lose or forget your password.

8.  Write down the recovery key and put it in a safe place in case you forget your password.

9.  Click Continue.

10.  Next, a dialogue box will appear asking if you want to store your recovery key with Apple. Select either “Store the recovery key with Apple” or “Do not store the recovery key with Apple” and click Continue.

• If you chose “Store the recovery key with Apple,” which will allow you to retrieve your recovery key from Apple if necessary, continue to step 11.
• If you chose “Do not store the recovery key with Apple”, which means you must keep a record of your recovery key in case it is needed, skip to step 15.

11. If you selected “Store the recovery key with Apple”, you will be asked to answer three security questions.

12.  Select the security questions from the security menus.

13.  Type your answer to each question in the corresponding text box.

14. Click Continue.

15. Click “Restart” to restart the Mac and begin the encryption process dialogue box, click Restart.

16. If you lose your password or do not remember your recovery key, visit the Apple Support page on FileVault.

Creating an encrypted disk image to store files

An encrypted disk image works just like a regular disk image but requires a password to open and become available (“mount”). You can move files to or from an encrypted disk image as easily as you can from a non-encrypted disk image. Follow these steps to create an encrypted disk image:

1. Open Disk Utility (located in /Applications/Utilities/).
2. Click the New Image button, or choose File > New > Blank Disk
3. ImageType a name in the Save As field. This name will be used for the disk image (.dmg) file.
4. Change the save destination if you wish.
5. Select a size for the disk image file from the Size pop-up menu.
6. Choose a different volume format if you don’t want to use the default Mac OS Extended (Journaled)
7. Choose an image format. You can use “sparse disk image” for a disk image that only uses as much space as it needs, rather than a set amount of space. If you’re not sure, use “read/write disk image” choice
8. Choose 128-bit AES encryption (and/or 256-bit AES in Mac OS X v10.5 or later) from the Encryption pop-up menu to encrypt the image’s contents with a password. If you don’t choose an encryption, your new image won’t be encrypted.
9. Click the Create button.

Enter and verify a good password in the dialog window that appears. This password will be saved in your keychain by default, or you can deselect “Remember password (add to keychain)” if you don’t want it saved. You can store the password in the keychain for convenience.

Click OK.

Important: If you forget the password, data stored in the encrypted disk image cannot be retrieved. If you have saved the password in the keychain, the password will be available to you there.