Two-step authentication is an authentication method that protects an account by performing another authentication (the second step) after the authentication by ID and password (the first step), such as when logging in. It is said to provide better security than ordinary one-step authentication.
For example, you can enter your ID and password and then enter the answer to a secret question, or you can enter an authentication code sent by SMS or email, or an authentication code given by phone.
Even if you are able to manage your login information perfectly, your login information may somehow fall into the hands of a malicious third party, and thus ID and password authentication (single-step and single-factor) alone is not secure. Therefore, two-step or two-factor authentication is becoming a mainstream solution.
With two-step verification, even if your login information such as ID and password is known to others, you can prevent unauthorized login and hijacking by blocking the second step of verification.
Moonstake recommends the use of Google Authentificator.
Learn how to use it here.