This tutorial guides developers to build an SMS-based word guessing game using Node.js, Express, and Twilio. The app sends an SMS with a mystery word, and players try to guess individual letters until they correctly guess the entire word or run out of lives. The code includes helper functions for handling game logic, such as checking if a message is a valid guess, processing correct guesses, and ending the game when a player wins or loses. The app uses Express sessions to store game state, including the mystery word, number of lives, and flag indicating whether a game is in session. Developers can test the app by sending SMS messages with "start" to begin a new round and guessing letters one by one until they correctly guess the entire word or lose.