The app uses the Strava API to access user data, a few-shot prompt templating approach with OpenAI and LangChain, and Streamlit for web application development. It generates a personalized marathon training plan based on the user's previous runs and activities. The app includes features such as email sending with Twilio SendGrid, PDF generation, and validation of user input. It also allows developers to experiment with different agents, prompting, and parameters to improve the output.