Google PageRank is an algorithm used by Google to rate web pages. There are many elements which influence the PageRank calculation, the main one being the number of and quality of links that a website has to other sites.
A website increases PageRank by creating links to other web pages; each link acts as a vote of confidence for your site. PageRank increases providing the links that are built are to other pages which also have a good PageRank’s. PageRank is scored between 1 and 10, 10 being the epitome of a perfect website. A PageRank for websites to aim for is 3 – 4 as this is what Google considers to be a good quality website.
It is important to create backlinks to reliable sites naturally. However, many companies deal in the practice of buying unnatural and unreliable backlinks in an attempt to artificially improve PageRank. This is a black hat method of SEO and should be avoided otherwise it may result in these links being ignored by the algorithm, or even more severely a Google penalty.
Links transfer power and reliability between websites. In order to increase your PageRank, you need to have links from external sites to your website, but ideally need to avoid putting outgoing links to sites on your own site. This is because an incoming link provides your site with power, whilst an outgoing one takes this away.
PageRank itself is not a big contributor to SEO success as it measures the importance of your website, rather than its relevance to different keywords. You do need to have a PageRank in order to be indexed in Google, but do not necessarily need a good page rank to succeed with SEO strategies.