This tutorial demonstrates how to use LaunchDarkly and Fastify to provide a customized user experience based on the users' email addresses. It covers setting up a development environment with Node.js, installing dependencies, configuring credentials, creating segments and flags in LaunchDarkly, serving static pages from Fastify, and using LaunchDarkly flags in a Fastify application. The tutorial also explains how to target different user segments based on their email addresses and provides additional resources for learning more about LaunchDarkly feature flags.