Module 1 introduced the explorer: the crawler that discovers the web by following links, and the shop on a street with no signposts that barely exists. That lesson was mostly about other sites linking to you — which you cannot control, and which Module 4 will cover. But there is a whole network of signposts you control completely, can publish instantly, and pay nothing for: the links between your own pages.
Three jobs, one click
Every internal link quietly does three jobs at once.
Job 1 — it guides the explorer. The crawler discovers your new page the same way it discovers everything: by following a link from a page it already knows. A new page with internal links pointing at it gets found on the crawler's next visit. A new page without them waits for the sitemap — and looks unimportant even once found.
Job 2 — it spreads reputation. Module 1 listed reputation among the big ranking signals. When other sites link to your homepage or your best article, those pages accumulate authority — and every internal link passes a share of it onward, like current through wires. Your strongest pages can lend strength to your newest ones. This is why the pros obsess over linking from their most-visited pages, not just to them.