The structure of a website refers to the website's organization, that is, how the individual subpages of the website are linked to each other.
Search engines prefer well-organized websites. Particularly with larger websites that have a large number of subpages, it is important that the crawlers find all of the subpages quickly and don't miss any.
For this reason, the home page of the website should link to the most important subpages first and foremost. Additionally, files like sitemap.xml and robots.txt, for example, simplify the work of the crawler.