This tutorial teaches how to implement a WhatsApp user verification flow in a JavaScript application using Node.js and Express, with Twilio Verify service. To start, create a new Twilio Verify service and install the required dependencies for the project, including Express, session middleware, dotenv, and Twilio's Node Helper library. Then, define an HTML page that asks users to enter their WhatsApp phone number, which is sent to Twilio Verify for verification. Once the user provides a phone number, Twilio sends a verification code via WhatsApp, which can be entered on the application's /verify page. If the code matches, the user is redirected to a success page with a message indicating they have been verified. The tutorial also covers how to use environment variables and .env files for secure configuration management.