It is simple to turn it on. To do so, navigate to http://appleid.apple.com/.
- Click "Manage your Apple ID"
- Log on
- Click "Password and Security"
- Follow the prompts under Two-Step Verification.
- Your Apple ID and password
- You must have your security questions and answers set up
- Once you turn on 2-Step Verification (and you will receive notification of this on the web site before you turn it on), each app on your phone/tablet will have an app-specific password to access your iCloud. This makes sure only apps you authorize can get to your account. Also, you will have a recovery key - a sequence of letters and numbers - that you will need to remember somewhere. I recommend placing it in your safe (a printed copy), or on a piece of paper in your wallet, or some such location. You will get it from the web site, at which point you can print it out, then will be prompted to re-enter it to verify that you have it.