How+does+SEO+work?

Search engines perform several activities in order to deliver search results – //crawling//, //indexing//, //processing//, //calculating relevancy//, and //retrieving//. However, the first thing you need to know to learn SEO is that search engines are not human. Unlike humans, search engines are text-driven. Although technology advances rapidly, search engines are far from intelligent – they don’t have emotional reaction to sights and sounds. Instead, search engines crawl the Web, looking at site terms and text to get an idea what a site is about. First, search engines crawl the Web to see what is there. This task is performed by a piece of software, called a //crawler// or a //spider//. Spiders follow links from one page to another and index everything they find on their way. Having in mind the number of pages on the Web (over 20 billion), it is impossible for a spider to visit a site daily just to see if a new page has appeared or if an existing page has been modified.
 * How does SEO work? **

As a webmaster, you need to check what a crawler sees from your site. As already mentioned, crawlers are not humans and they do not see images, Flash movies, JavaScript, frames, password-protected pages and directories. If they are not viewable, they will not be spidered, not indexed, not processed, etc. This will not help your ranking.

After a page is crawled, the next step is to index its content. The indexed page is stored in a giant database, from where it can later be retrieved. Essentially, the process of indexing is identifying the words and expressions that best describe the page and assigning the page to particular keywords. For a human it will not be possible to process such amounts of information but generally search engines deal just fine with this task. Sometimes the meaning of a page will be incorrect. That’s where SEO is important. If you work to optimizing your pages, it will be easier to classify your pages correctly which results in higher rankings. When a search request comes, the search engine processes it – i.e. it compares the search string in the search request with the indexed pages in the database. Since it is likely that more than one page (practically it is millions of pages) contains the search string, the search engine starts calculating the relevancy of each of the pages in its index to the search string.

There are various algorithms to calculate relevancy. Each of these algorithms has different relative weights for common factors like keyword density, links, or metatags. That is why different search engines give different search results pages for the same search string. It is a known fact that all major search engines, like Yahoo!, Google, Bing, etc. periodically change their algorithms. So if you want to keep at the top of search results, you need to adapt your pages to the latest changes.

The last step in search engines' activity is retrieving the results. Basically, it is nothing more than simply displaying them in the browser – i.e. the endless pages of search results that are sorted from the most relevant to the least relevant sites.