According to SEO guidelines when a search engine crawls a particular site it processes each of the pages it crawls in order to compile a massive index of all the words it sees and where they are located on each of the pages. Also search engines will process information included in key content tags and attributes, such as title tags and ALT attributes. Search bots process many, but not all, content types. For example, they cannot process the content of some rich media files or dynamic pages. How search engines display search results, when a user enters a query, search machines search the index for matching pages and returns the results that they believe are the most relevant to the user.

Relevancy is determined by Google by over 200 factors, the most important one being Page Rank is the measure of the importance of a page based on incoming links from other pages. Basically each link to a page on your website from another site adds to your site's page rank. Not all links are created equal and so Google works hard to improve the users experience by identifying links that are considered spam links which are links that are purchased from a link farm or generated from a linking program. both of which are of no value to your page ranking. The best types of links are those that are given based on the quality of your websites content.