Search engines find and sort info through three main ways:
1. Crawling: Spiders are automated systems that search engines use to “crawl” the web, checking each link they come across and finding new sites for the search engine to list.
2. Indexing: After the spider has crawled a page, that page becomes part of the Google index and the content of the page is analyzed for the purposes of ranking.
3. Ranking: The way search engines use algorithms to rank content is the aforementioned complicated and mysterious part of the system. The words on the page, the structure of the site, the number of links referring to the site, and many more factors all come into play to determine which keyword searches will return the page as a result, and how high up in the results the site will go.
Courtesy of: Collis Ta’eed