Linkbuilding is the process of establishing links within your own site and between your site and other sites.
Because hyperlinks in your content enable a user to learn more information about a certain topic or further investigate a source, the user experience is improved.
Because hyperlinks from other sites that direct users to your site indicate credibility, search engines see links as a good sign.
Search engines use links as the tunnel to crawl through the web and discover new pages to index. They also use links to assess pages for purposes of SERP ranking.