This tutorial guides users through setting up a private call system using Nexmo's Voice API, forwarding calls via a voice proxy, and adding a recording feature. To begin, users need to install Node.js and Node-RED, create a Vonage API account, and obtain necessary credentials. They then set up their local server to be accessible over the public internet using ngrok. Next, users create a Nexmo Voice Application, link a virtual number to it, and define a webhook endpoint for inbound calls. The tutorial provides instructions on how to handle incoming calls, log call events, and add a recording feature to the system. Throughout the process, users learn about various Nexmo APIs, Node-RED nodes, and NCCOs, which are used to control the flow of the call. By following this tutorial, users can create a private call system with recording capabilities, making it suitable for businesses or individuals who need to make secure calls without revealing their phone numbers.