The article covers the process of building a multi-tenant link shortening application using Phoenix and Elixir. It outlines the importance of multi-tenancy in modern web applications, the prerequisites for the project, including installing Elixir, Phoenix, and PostgreSQL, and details the steps to create the application. The guide includes insights on different multi-tenancy strategies, the PETAL stack, and focuses on a shared database with a shared schema approach for simplicity and scalability. It also guides through setting up multi-tenancy, creating contexts for accounts and users, and integrating user authentication through the Pow library.