This tutorial demonstrates how to play an audio file into an active call programmatically using the Vonage Voice API and Node.js. To start, users need to install Node.js, set up a Vonage API account, rent a virtual phone number, create a voice application, initialize dependencies, make the application available on the public internet, configure the environment, run the application, and understand how it works. The logic happens in server.js, where the application instantiates the Vonage client library, serves audio files and NCCO (Call Control Object), makes an outbound call, plays audio into the call, and disconnects the call after a specified time. The tutorial provides a step-by-step guide to integrate voice capabilities into web applications using Node.js.