what makes a website pr1 pr2 .. pr10?

I want to start taking action and begin link building, but I don't know how to distinguish between a low PR site and a High PR site.
What differentiates a PR1 from a PR10? Is there an easy way to find out which is which?

Any help would be appreciated.

Thats quite a question! Use mozzila ...Install Google Tool bar (or any other tool bar which shows Page Rank) and then you will be able to know whats the PR of a site ...

i use searchstatus firefox plugin and it shows the PR of each site opened in your browser in the status bar

There are lots of tool you can use to know the pr of a site.

You can download and install Google Tool Bar on your system
and you will see information of any site you visit and PR or
use services like SEOCENTRO dot com to check the PR of a site.

Just to let you know, PR by itself is nothing and does not
play any significant role in ranking...