Your email address is the center of your security world. It is highly recommended that you enable Two-Factor Authentication to minimize risk of someone accessing your email through spear phishing attack, discover caches of passwords in your mailbox, and other related email attack. As an example, the attacker of DNC email uses a simple password reset request through spear phishing attack, was able to gain access to the email and password. If the Two-Factor Authentication is enabled, it will require another layer of security through verification code and stop it.
Two-Factor Authentication or 2-Step Verification adds an extra layer of security to your email account by requiring you to enter a verification code in addition to your username and password when signing into your email account. It help protect a user's account from unauthorized access should someone manage to obtain their password. Even if a password is cracked, guessed, or otherwise stolen, an attacker can't sign in without access to the user's additional verification. This verification can be in the form of codes which only the user can obtain via their own mobile phone.
Requirement. To use Two-Factor Authentication you need to have a mobile phone that can receive the verification code via text message or phone call. Other devices use the Google Authenticator mobile app to generate the verification code.