Q: How do I get two factor authentication?

You will likely have to wait for it. It is being rolled out gradually -- apparently quite gradually. See the quote below from Availability of two-factor authentication in iOS 9 and OS X El Capitan - Apple Support

With hundreds of millions of users in the Apple ecosystem using a variety of devices and software versions, this will take time. To ensure the best experience possible, we'll roll out two-factor authentication gradually starting this fall.

Two-factor authentication will be made available to users who meet the system requirements below on all the devices they use with their Apple ID.

• iPhone, iPad, or iPod touch with iOS 9
• Mac with OS X El Capitan and iTunes 12.3
• Apple Watch with watchOS 2
• Apple TV (4th generation) with tvOS
• Windows PC with iCloud for Windows v.5 and iTunes 12.3

Other criteria will also be used to determine availability. So even if you meet all the system requirements, you might not be offered two-factor authentication right away. We'll increase availability over time, until we can offer the feature to everyone.

The above link gives more information including how to check to see if it is available for your Apple ID. If it is not, you can still use two-step verification instead and it offers very similar protection. Frequently asked questions about two-step verification for Apple ID - Apple Support