This article explains how to build an application using .Net MVC 5 and Twilio to make and receive phone calls. The author starts by setting up a new ASP.Net Web Application, adding a controller, and configuring ngrok to expose the local environment to Twilio. Then, they hook up a Twilio telephone number to their application, creating a webhook that will trigger when someone calls the number. They also implement a handler for receiving calls and making outgoing calls using the Twilio Rest API. The author provides code examples throughout the article, including how to store account information as environment variables and how to create an IVR system with the Gather verb.