Every module is a single page. Read it, take the 3–5-question quiz, click Next. Quizzes never block — they just record your score so the certification page can summarize what you learned. Progress lives in your browser's localStorage; nothing is ever sent anywhere.
Tier 1 is daily-driver porcelain. Tier 2 is the helper layer. Tier 3 is the plumbing — the content-addressable filesystem that everything else is built on. Read in order if you're new; jump around if you're not.
Toggle the theme top-right (dark / light). Print any page for a clean black-on-white version — including the certification page when you're done.