This document introduces Flask, a Python microframework for building web applications and APIs. It shows how to create a basic "Hello World" Flask app in 3 steps: creating the Flask object, defining a route, and returning a JSON response. It then demonstrates various response types like simple text, generators, and files. It covers routing concepts like dynamic routes, default values, and REST verbs. More advanced topics discussed include static file serving, database connections, exception handling, and using blueprints to organize routes.