Before going more deeply in Search engine Optimization topic you need to understand working of search Engine first. If you understood working of Search Engines then you can learn SEO more deeply.
How Search Engine Works?
Search Engine works on 3 main steps.
There are billions of websites and there pages. Search Engine Crawlers is algorithmic program which is used to crawl the pages. Search Engine Crawlers have responsibilities to decides which pages of which websites need to be crawl. Crawlers also decides crawling frequency.
Crawlers collect URL of pages from websites and put them into web page cache. Crawler also gets URL from sitemap.
Search engines crawlers detects dead links, new websites link, any changes in pages etc. and send it to indexing.
See what Matt Cutts says about crawlers
“Crawlers starts by fetching a web pages and then they follow the link on those pages and fetch the pages they point to and follow links on those pages and fetch the pages they links to and so on, until Google have index a pretty big chunk of the web. Many billions of pages stored across thousands of Machine.”
Search engine bots processes each page, compiles the words, location. Also processes keywords, Alt tag attributes etc.
Search engines cannot index rich media files.
When user submits query search engines finds related indexed pages which are matching with query and rank them by considering Ranking SEO Factors.
Search engine works their best to serve the best result to users.
Most important ranking factor is Page Rank. Page rank is based on number of incoming links from other sites.
See what Matt Cutts says about Serving results.
“After Submitting query by user, Google software searches Google index to find every page that includes those search terms. There are hundreds and thousands of possible results. Then how Google finds relevant result?
Google checks those 200+ SEO factors. Like how many times those search terms appearing on webpage? Do those searched words appeared in title, in URL and any other keyword places? Does page contain synonym of search words. Is the page is high quality or low quality or spamming? What is page rank of the page?
Finally Google search engine combines all those factors togather to produce each pages overall score and sends back to search Engine result page within half of seconds after submitting a query by user.”
reference from: Google support .
Recommended link how search works
See this video created by Matt Cutts to learn more about How Search Engine Works.