PageRank is only a score that represents the importance of a page, as Google estimates it (By the way, that estimate of importance is considered to be Google’s opinion and protected in the US by the First Amendment. When Google was once sued over altering PageRank scores for some sites, a US court ruled: “PageRanks are opinions — opinions of the significance of particular Web sites as they correspond to a search query….the court concludes Google’s PageRanks are entitled to full constitutional protection.)
The majority of web traffic is driven by the major commercial search engines, Google, Bing, and Yahoo!. Although social media and other types of traffic can generate visits to your website, search engines are the primary method of navigation for most Internet users. This is true whether your site provides content, services, products, information, or just about anything else.
Paid-for links and ads on your site MUST have a nofollow attribute (see Google’s policy on nofollow). If you have paid links that are left followed, the search engines might suspect you are trying to manipulate search results and slap your site with a ranking penalty. Google’s Penguin algorithm eats manipulative paid links for lunch, so stay off the menu by adding nofollow attributes where applicable.
An SEO technique is considered white hat if it conforms to the search engines' guidelines and involves no deception. As the search engine guidelines are not written as a series of rules or commandments, this is an important distinction to note. White hat SEO is not just about following guidelines, but is about ensuring that the content a search engine indexes and subsequently ranks is the same content a user will see. White hat advice is generally summed up as creating content for users, not for search engines, and then making that content easily accessible to the online "spider" algorithms, rather than attempting to trick the algorithm from its intended purpose. White hat SEO is in many ways similar to web development that promotes accessibility, although the two are not identical.
Webmasters and content providers began optimizing websites for search engines in the mid-1990s, as the first search engines were cataloging the early Web. Initially, all webmasters needed only to submit the address of a page, or URL, to the various engines which would send a "spider" to "crawl" that page, extract links to other pages from it, and return information found on the page to be indexed. The process involves a search engine spider downloading a page and storing it on the search engine's own server. A second program, known as an indexer, extracts information about the page, such as the words it contains, where they are located, and any weight for specific words, as well as all links the page contains. All of this information is then placed into a scheduler for crawling at a later date.