Can someone help me to understand PR. Why is it so important? How is it determined? Thanks in advance
The basic short summary of page rank would be it's the ranking of a site from 0 to 10, that the google algorithm determines is the popularity of your site. It's not an exact science (ie. do this and you get page rank 7), but the basic idea is the more links from other sites to your site shows google your site has some use. If you want to up your page rank, write good content people want to read (and link) as well as work on getting your site linked from other sites. These forums have TONS of ideas on how to accomplish both, so just take some time and search around.
One of the best article i found on page rank is this, http://en.wikipedia.org/wiki/PageRank history of pagerank from start to end
Here's the official line: http://www.google.com/technology/ Don't sweat over PR too much - a lot of hype, not much substance.
google's algorithm is different from all other search engines. Mainly Google checks the out bound links and also incoming links for that site. They give PR
PR is also heavily used for determining how frequently Google will crawl your pages, and how deep it will crawl. Higher PR = more frequent/deeper crawls. I always consider it a "Priority Rank" instead of "Page Rank", since this is how Google's servers utilize it.
PR is determined by links to and from your website. The quality of the links is more important than the quantity. More than PR I would suggest you to concentrate on getting good SERPs for your website's targeted keywords which would be more beneficial in the long run.