PR stands for Popularity Rating (or maybe popularity ranking – I’m not quite sure)
So to get a higher ranking get more people linking to your sites.
The quality of the links matters too – that is to say if they sites linking to you have a higher PR than you – then it will help to boost your own PR.
Bear in mind though that other than in forums like this it is hard to tangibly state what benefits the PR gives you.
PR does not seem to be a major factor in most of Google’s SERPs .