The guide covers sending a single SMS message using Twilio and Node.js, and then scaling up to send multiple messages with a messaging service. The author uses an ice cream delivery scenario to illustrate the process, starting with a simple example of sending one message and gradually increasing complexity as the number of subscribers grows. The guide introduces three tools: regular API calls, messaging services, and Twilio Notify, which allows for sending hundreds or thousands of messages in a single API request.