Learn to create and deploy a simple "Hello World" web application using Flask and Heroku in this 25-minute tutorial. Explore the basics of Flask, including HTML templating, CSS styling, and Python backend development. Follow step-by-step instructions to set up the Flask directory structure, create an HTML template, implement a Python backend, add message flashing functionality, and apply CSS styling. Discover how to troubleshoot common issues like CSS not updating and the importance of clearing cache. Finally, prepare the necessary files for deployment and learn how to deploy the Flask app on Heroku for free. Gain practical experience in web development and deployment, suitable for beginners in Python GUI programming.