via sms
Most of the social apps send SMS to your personal number every time you log into your account. The code that is sent is one-time, therefore it is only used once. Through them, it is quite convenient, because they can only log into your account if they have access to your mobile phone and know your password, so you reduce the likelihood of a cyber attack.
via email
The principle is the same as that via sms. A verification code is being sent to your email.
via application