Two-step verification is an optional feature that adds more security to your account. When you have two-step verification enabled, any attempt to verify your phone number on WhatsApp must be accompanied by the six-digit PIN that you created using this feature.
To enable two-step verification, open WhatsApp > Settings > Account > Two-step verification > Enable.
Upon enabling this feature, you can also optionally enter your email address. This email address will allow WhatsApp to send you a link via email to disable two-step verification in case you ever forget your six-digit PIN, and also to help safeguard your account. We do not verify this email address to confirm its accuracy. We highly recommend you provide an accurate email address so that you're not locked out of your account if you forget your PIN.
Important: If you receive an email to disable two-step verification, but did not request this, do not click on the link. Someone could be attempting to verify your phone number on WhatsApp.
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 PIN. Thus, if you forget your own PIN, 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 PIN, 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 PIN, your account will be deleted and a new one will be created upon successfully reverifying.
Note: To help you remember your PIN, WhatsApp will periodically ask you to enter your PIN. There is no option to disable this without disabling the two-step verification feature.