Google offers 2-Step Verification to protect the security of user accounts.
1. First, log in to your Gmail account as you usually would.
2. Click on the icon in blue in the upper right-hand corner, and select Account. This will take you to your Account Settings page.
3. Scroll down to the Signing In section and you will see 2-Step Verification listed as “Off.” Click on 2-Step Verification. You will be directed to this page, click start setup.
4. Set up your phone number with Google if you have not already done so. Enter your number in the field provided and click Send Code.
5. Enter the verification number Google sends you in the field provided and click Verify.
6. If you trust the computer you are using in this setup process, check the box labeled “Trust this computer” and click Next.
7. You are almost done! Now that you’ve set up your number and trusted device with 2-Step Verification, click Confirm to finalize the process.
8. You should be redirected to this page, and you will see that 2-step authentication is ON.
For more information visit: http://www.google.com/intl/en-US/landing/2step/features.html