The article offers a detailed walkthrough on building and deploying a simple Flask application that compares the weather of two cities using the OpenWeatherMap API, as part of the 100DaysOfCode Challenge. The author explains each step, from setting up a virtual environment and installing necessary dependencies to obtaining an API key and writing the core application logic, which includes fetching data from the OpenWeatherMap API and rendering it using a Flask template. The app's user interface is enhanced with PureCSS for a clean design, and its functionality is streamlined with helper functions for time conversions and API queries. The article also covers the deployment process to Heroku, describing how to configure the Heroku environment, set environment variables, and manage the application's deployment lifecycle. The author encourages readers to experiment with creating their own Flask applications and participate in the ongoing Flask Code Challenge.