Once you've agreed all the terms and conditions and downloaded the software, it should appear in the menu bar of your browser.
At the extreme right hand side of the bar click 'settings' then select 'Options' from the drop down menu. In the dialogue box select the tab 'more' and tick the box 'PageRank'. Click 'OK' to accept and then 'OK' to close the dialogue box.
Now browse to your website and check out it's PageRank.
Don't worry if it's only 2/10 or 3/10, that's not the end of the world you can make some improvements, but bear in mind that the BBC is only a 9/10.