There's a lot of bad SEO advice out there. Partly because it's all outdated. There was a time where you could play lots of little keyword tricks to convince search engines to send you more visitors for keywords you care about. But those times are mostly over now.
Today it mostly comes down to building authority on certain topic and having high quality relevant information for those topics.
Search engines crawl your website and save information about your webpages into their database. Looking at the words and sentences on a webpage, they can determine if it's relevant for what the searcher is searching for.
If you have multiple pages and articles on your website talking about the same topic, it's an additional hint to the search engine about relevance of your website in relation to the searcher's query.
This is a much more complex decision for the search engine. There are many factors that go into this: