The theory is that Google gives high page ranking (PR) to quality and authorative sites. One way Google knows if a site is any good is if it has links from high PR sites, preferably relevant to your site. This is seen as a vote in your favour. The more you have the higher you go up the rankings. One way of getting links is to write articles and submit them to good article directories such as Ezine Articles. You will have a Resource Box at the bottom of the article and you put a link in that. If you are no good at writing there are people who will write articles for you for a few dollars. You just have to keep at it and get a lot of articles in a lot of high PR directories. If you sites are very new you will start at PR0 until Google has checked them out and given them a ranking. Hope this helps.