Page Rank is an analytic that quantifies the worth of a particular page within your website, the search engine algorithm has set metrics to measure a page and its worth.
First the algorithm will analyse the URL, meta data and title of the page, it will then proceed to read the content within the page paying close attention to the use of heading tags throughout your page, this is an important factor as the visually impaired and blind use this function as a method of easily navigating your website.
All of the above must flow organically, as an example if your written content is about a sport and your title and meta content is nothing relevant to sport then they do not match up and will suffer.
Bare in mind Google and other search engines are becoming ever more sophisticated and have millions of phrases entered on a daily basis, so if your website was about the sport of football the following words would be associated, ball, referee, stadium, team names, players, scores, league tables, fixtures and so on. So although these words do not need to appear in the title or meta data the search engine can associate them to your website as they know searches in the past have been conducted with these words attached to football.
In years gone past and to this day people assume that because they have a link from a website with a high page rank then they will benefit with more of what is referred to as (link juice) this is simply not the case, for one you could have a link for a site it a page rank of 5, but that site could be linking to several other sites severely diluting your juice.
Let’s take the above example and pretend we have a website about football, now we have obtained 2 links, the first is from a small local amateur football club with a page rank of 1, the second link if from a tech website that enjoys a page rank of 5.
With the above example many would assume you would gain more link juice from the tech website in truth you would gain more from having a link from the amateur football club with a page rank of 1. Why?, because the amateur football club will have a list of keywords and content that is relevant to your website, whereas the tech site will not.
So page rank is important but the most important think is link value.
What is link value? As explained above the algorithm metric will not only look at a websites page rank but will look to determine the value of the link by crawling the page that is linking to you.