Varnish Cache is a web application accelerator that can speed up websites. It works by caching content and serving it to subsequent requests, reducing load on backend servers. The document outlines 9 steps to implement Varnish Cache, starting with easy steps like caching static assets and compression, then progressing to more complex techniques like caching semi-static content, graceful degradation, and advanced invalidation methods using custom headers. Implementing the initial steps provides minor speed improvements, while fully utilizing Varnish Cache through techniques like content composition and invalidation can yield high performance gains.