Understanding Google PageRank: Infographic | visualizing social media | Scoop.it
PageRank is basically a score given to your site that rates its overall popularity. Now, a high PageRank does not always translate into a high ranking, but it does play a part. For instance, if your website is as optimized as your competition's site, but yours has a higher PageRank, you will likely rank above the site you are competing with. PageRank helps build a foundation for success just as proper on-page optimization does.

To improve your PageRank, you should try to get inbound links from other sites that already have a high PageRank. While you could go get hundreds of links from sites with a PageRank of zero, they will not count as much as a few good links from PageRank 5 or higher sites...