David Prothero provides a comprehensive guide on building an SMS-based app using C#, ASP.NET, and Azure, designed to help users find their federal representatives by ZIP code. The project utilizes Microsoft tools alongside the Twilio API and the Sunlight Foundation's Congress API to process text messages and return representative details. After setting up an ASP.NET MVC project, users install necessary NuGet packages and create a Legislator controller that integrates with the Congress API to fetch data. The app processes incoming messages to extract ZIP codes, queries the API, and formats the response to inform users about their legislators. The guide covers local testing using PowerShell and deployment on Azure, with instructions to configure a Twilio phone number for handling SMS messages. The complete source code is available on GitHub, allowing readers to further customize and deploy their application.