Mallory Mooney guides the reader through a step-by-step process of using Datadog to collect metrics, request traces, and logs from a Rails application running on Passenger, Apache, and MySQL. The guide covers installing and configuring the Datadog Agent, capturing logs, enabling integrations with Apache and MySQL, creating custom dashboards and alerts, and fine-tuning log collection for maximum visibility into your application's performance and infrastructure. By following this guide, developers can gain a comprehensive view of their Rails stack's health and troubleshoot issues more efficiently.