Server-Side Rendering (SSR) was introduced in Gatsby 4 in 2021, allowing developers to render HTML on the server for use cases like dynamic personalization and improved search engine indexing. This walkthrough explores the ease of implementing SSR in Gatsby, using a demo app that displays cat images. The demo app involves a client-rendered index page and a server-rendered demo page, where the latter uses SSR to fetch and display additional data about the cat images. The project setup includes using Node.js, npm, and a code editor, with options for deploying to Gatsby Cloud. The process includes configuring the development environment, creating Gatsby pages, and using the Cat-as-a-Service API for image data. The article also covers deploying the finished project to Gatsby Cloud and provides insights into using SSR in Gatsby projects.