This tutorial guides developers through building a voicemail system using Express.js and Socket.io, integrating with the Vonage Voice API to enable call handling, event processing, and real-time updates for voicemail messages. The project utilizes ngrok to expose the local development server to the internet, allowing it to be accessed remotely. A virtual phone number is also linked to the application to facilitate incoming calls. The system includes routes for answering calls, processing events, and saving voicemails, with a user interface that displays received voicemail messages in real-time using Socket.io connections.