This tutorial guides users in building a phone number lookup app using Vonage's Number Insight API, which provides basic, standard, and advanced lookups for information about a phone number such as carrier, country, and more. The app is built with Node.js and Express, allowing users to input a phone number and retrieve details through an intuitive user interface, with the complete source code available on GitHub. To use this tutorial, users need a Vonage API account and will follow a step-by-step process of setting up their project, installing dependencies, adding environment variables, building the server and front-end, and running the application. The app provides valuable information about phone numbers, including validity, reachability, and roaming status, allowing developers to expand on this knowledge and build upon what has been learned today.