This tutorial guides developers to build an expense tracker application using Symfony and MySQL with the help of PlanetScale, a MySQL-based database platform that simplifies database development and provides scalability and hassle-free migrations. The application allows users to create new expenses, view all expenses, and visualize their spending in a pie chart. Throughout the process, developers learn about setting up a database, configuring the Symfony application, creating forms for expense creation, seeding data, and rendering templates with Bulma styling. By following this tutorial, developers can build a robust and scalable web application using Symfony and PlanetScale.