Bare in mind this is only a brief expanation of Google’s PR.
Web pages picked up by the Google database are, if valuable, are given a “page Rank”
Among the multitudes os variants Page rank uses a formula as follows:
PR(a)=PR(b)/links(b) + PR(c)/links…..PR(n)/links(n)
Basically the number of other web pages that point to your page. The equation was formulated by Google’s co-founders Larry Page and Sergey Brin as grad students at Stanford University.
Page rank in a nutshell is a popularity vote. When other pages point to yours. But the equation tells us something else as well. If the site pointing to your site has numerous of links pointing to it the better your link exchange or cross link will perform.
For example, say for my web site, If I had the New York Times link to my site I could technically only rely on this one link and my PR would be five of greater. The reason would be the New York Times has alot of other web pages linking to it, making it a more valuable. Consider also the age of the site. The New York Times web site has been around for along time giving other sites lots of time to link to it. It would apppear the age of the site has alot do with PR as well.
Getting sites to link to yours is excellent to achieving a high PR. But be cautious, it better to do a link exchange with an aging site that has alot of inbound links. Linking to site that just have alot of other links on their site does not me it would be a valuable link exchange.
For exchanging links or called cross linking, link with sites that are revelant to yours. But if its a site just linking to your site it is valuable to a certain degree. One way links are the way to go, buying one way links are becoming a dangerous. Google as of late does not like this practice.
So to conclude:
PageRank is a numeric value that represents how important a page is on the web. Google figures that when one page links to another page, it is effectively casting a vote for the other page. The more votes that are cast for a page, the more important the page must be. Also, the importance of the page that is casting the vote determines how important the vote itself is. Google calculates a page’s importance from the votes cast for it. How important each vote is is taken into account when a page’s PageRank is calculated.
PageRank is Google’s way of deciding a page’s importance. It matters because it is one of the factors that determines a page’s ranking in the search results. It isn’t the only factor that Google uses to rank pages, but it is an important one. From here on in, we’ll occasionally refer to PageRank as “PR”.
This is a huge topic enough to write a book on. Google PR 0-4 are considered unimportant sites, PR5-10 are important to Google.
I hope this helps. There is more but my time is limited. Thanks greek39