Describe the algorithm of two-factor authorization on the site?

Question

User identification

From A to Z desirable. I came across such a task in a test task.

Answer 1

Only after entering the correct user password in the user authorization form on the service (or in the application), the service sends a one-time service password (this is NOT a PIN code!) to the user via the communication channel selected in advance by the user (mail, sms, etc.), which must be entered in another field in the authorization form.
If the user password and the service's one-time password are correct, the user is successfully authorized on the service. Otherwise - no.