• A Search engines aim (other than to make money) is to deliver the most relevant search results for your search keywords.  Search engines are able to deliver results blisteringly quick as they search their database (index) of the web.
• Search engines use crawlers to visit each page on your site and extract key information from your web pages to build a better understanding. Google's index is 100,000,000 gigabytes and containes billions of webpages. It's equivalent to 195,312 iPhones with 512GB of storage! 
• If your website isn't known to search engines, then its highly unlikely your website will rank. 
• The order in which search engine result pages are presented to users are ordered by their algorithms. The algorithms have over 200 different ranking signals. 

When a search engine index your site, their system attempts to crawl through every page of your site and use information from your pages to add to their database (index) representing your website and your content. 

These complex search engine algorithms that are used to rank websites are kept under wraps by each search engine. Search engines themselves compartmentalise different components of their algorithm within their organisations and are run by different teams.