The latest update to WhatsApp beta lets you secure your account with a six-digit passcode. WhatsApp verifies your phone number via an SMS confirmation when you're setting up the service on a new phone, and with two-step verification enabled, you'll have to enter the passcode as well to gain access to your account.
You also get the option to add your email address, which can be used to disable two-step verification should you forget your passcode. If you're looking to go ahead and enable two-step verification, you'll have to consider the following:
If you have two-step verification enabled, your number will not be permitted to reverify on WhatsApp within 7 days of last using WhatsApp without your passcode. Thus, if you forget your own passcode, but did not provide an email to disable two-step verification, even you will not be permitted to reverify on WhatsApp within 7 days of last using WhatsApp.
After these 7 days, your number will be permitted to reverify on WhatsApp without your passcode, but you will lose all pending messages upon reverifying - they will be deleted. If your number is reverified on WhatsApp after 30 days of last using WhatsApp, and without your passcode, your account will be deleted and a new one will be created upon successfully reverifying.
WhatsApp doesn't verify your email address, so it asks that you "provide an accurate email address." The service will, however, periodically remind you to enter your passcode.
The feature is now live in the beta channel (2.16.346), and should make its way to the stable release soon. WhatsApp is picking up features at a steady pace, with the ability to make video calls going live on the platform in recent weeks.