Samsung two-step verification is an enhanced security feature that prevents someone from signing into your Samsung Account.
It strengthens the security by using two different authentication factors to verify your credentials: password, and an extra security code.
When signing into your account, you will enter your password and shortly after receive a verification code to your mobile phone via text message. If someone attempts to sign into your account with your password, they will not be able to access your account due to not receiving the additional verification code.
Learn more about this feature on the two-step verification page.