On-page refers to every element contained in the page structure, including the page title and content hierarchy, meta content, the page content, in-bound and out-bound links, page load speed, image optimisation, etc.
What do search engines look for when they crawl your website’s pages? They look at the ‘theme’ of the page which could also be explained as ‘which search queries does this page answer?’.
When the content of a page is decided, it’s time to conduct keyword research to determine the search terms people use when looking for the the page content. The page structure is then based around the most popular keywords or keyphrases which match the page content.