Look up "Matt Cutts" and "Pagerank".
Essentially, Pagerank is a value assigned based on the total value of the links coming in to your website. So, if several PR4 pages link to a page, that page should have a PR of 3.
Pagerank has value, but some folks really obsess way too hard about it. Truth is, the only real goal you should have for PR is to start out in the PR3 range. PR4 is good and PR5 is excellent. Anything above that is just a popularity contest.
PR helps to quantify popularity, but it's also important to work hard on good content and worthwhile keywords linking in to your website.
My advice: shoot for PR3, but focus heavily on content and driving real visitors to your content. The rest will take care of itself.