How to do 2 factor authentication?

Question

User identification

Hello. The project required 2 factor authorization.
How does this happen (meaning the interaction of the front and the back)?
That is, according to my logic: The
user enters a password and the login presses the confirm button, this data is sent to the back, some key is generated on the back and sent to the user to the specified mail, he inserts this key into the input, presses confirm, this key is sent to the back and checks with the fact that it was generated, if everything is fine, we let the user into the app.
If you have any articles or examples, please post them.
Technology stack:

• Frontend: React & Redux
  
• Back-end: PHP
  

Answer 1

The user enters a password and the login presses the confirm button, this data is sent to the back

The simplest form and handler.
Function for random key generation. For example, like this , but it's better to write your own.
The generated key must be placed in some type of database storage (and set the parameters for the expiration of the code, the owner of the code, the number of attempts to enter) and verify when the user enters.
Again the form and handler.

Answer 2

Better use 2FA from Google: https://www.google.ru/landing/2step/
Mail can be hacked (most users have the same passwords, even if you generate a password, many change it to the usual one), and in the case of 2FA from Google this option is excluded.