Introduction
Start here. What is Baseline? answers whether it is for you. What is Eleventy? is the ground floor underneath it, for anyone who has not built a site out of files and a text editor before. The quickstart gets you a running site, and the simple site tutorial walks the same ground with the reasoning visible.
From there, the concept chapter has the mental model behind the plugin and the small set of rules that keep Baseline out of your way.