This tutorial series is about integrating Twilio's ConversationRelay with OpenAI for real-time voice conversations. It covers setting up the environment, writing the server code, and adding tool calling to interact with external APIs. The tutorial assumes prior knowledge of Node.js and Twilio, and provides instructions on how to deploy the application using ngrok tunneling service. The series includes topics such as interruption handling, token streaming, and tool calling, which enable developers to build more interactive and engaging voice applications.