Sometimes there is confusion between the number given for PageRank and the SERP, Search Engine Results Position which is how far down the list your site appears in the Search Engine Results. Although backlinks play a part in your SERP, the actual number for the PageRank is awarded for backlinks only. Getting a low Page Rank does not necessary mean that you will get a low SERP. Its possible that your site is visted by many but there are very few back-links to your site, which will result in a very low PageRank or none at all but its your SERP that really counts.
PageRank indicates how many relevant reputable sites link back to your site, which in turn drives users to your site. Getting backlinks is also another channel for user access to you site .
The PageRank is from 0 - 10
Ian Rogers has a very good article The Google PageRank Algorithm and How It Works which explains in detail how the process works .
You can download a button for your browser that will show the Page Rank for any page: get button.
To give you some perspective on the rank you get for any of your pages here is the page rank for the portal page of some sites as of May 2012:
|The White House||9|
|A Site Apart||8|
|Made by Hand||4|
|3 Degrees Agency||3|