Internal Linking
Internal linking is the practice of placing links between pages on your own site, which spreads ranking signal from strong pages to weaker ones, helps search crawlers discover and understand related content, and guides readers from one relevant page to the next.
When one page links to another on the same domain, it passes along a share of authority and tells crawlers the two pages are related. Pages with no internal links pointing at them are hard to find and tend to rank poorly, no matter how good they are, so a page that earns external links can lift the pages it links to in turn.
The clearest way to use internal linking at scale is a pillar-and-cluster structure: one broad pillar page on a topic links down to several narrower cluster pages, and each cluster page links back up to the pillar and across to its siblings. This gives crawlers a tidy map of how your content fits together and concentrates relevance around the topic you want to rank for.
The honest caveat is that more links are not always better. Stuffing a page with dozens of internal links dilutes the value each one carries and can read as manipulative, so favour links that are genuinely useful to the reader, use descriptive anchor text rather than "click here", and fix orphaned pages before adding decorative ones.