The guide details a step-by-step approach to building a basic Spring Boot web application that displays weather information for Detroit, Michigan, while incorporating feature flags using Split.io. It begins by setting up necessary accounts and dependencies, including Split's Java SDK and the Open Weather Map API, before using the Spring Initializr to create the application's scaffolding. The process involves creating a simple HTML page to display weather data and implementing a controller to manage data retrieval, initially using hardcoded values, and then toggling between a stub service and a live weather service via feature flags. The use of feature flags offers dynamic switching between different implementations and introduces basic rules for split management, demonstrating how to enable or disable features seamlessly. The guide encourages further enhancement of the application by suggesting additional features like input fields for different locations, unit tests, advanced split treatments, and styling improvements, while also highlighting the broader potential of feature flags in application development.