SMS send tutorial

I am looking for a tutorial on how to create a server capable of sending sms (via an API or directly via a GSM modem and a SIM card) to verify a phone number by generating:

A random code

Store it locally

- send it to the server

- Send the phone number

On reception the server sends an SMS to the phone number with the code that the application to send.

The user must then enter the code in his application (it can also detect it on his own) to verify that it is correct.

 

Thanks!