Simon Grimm's tutorial on building a Twitter app using Ionic 2 guides developers through creating a simple application where users can log in with their Twitter accounts, view their timelines, and send tweets. The process involves using the Twitter Connect plugin from Ionic Native, which employs Fabric for integration, requiring Twitter App and Fabric API keys. The tutorial details setting up the project structure, configuring API calls with a custom provider, and implementing basic user interface components, such as a login page and tweet composer. Additionally, Grimm suggests the potential for packaging the Twitter provider into an NPM module for easier reuse and highlights the benefits of leveraging device-stored Twitter credentials for seamless user authentication. The tutorial emphasizes the practical application of these steps to enable interaction with the Twitter REST API directly from a mobile app.