How do I “sculpt pagerank” on my site?

Wow, this is a complicated question. Let’s start at the beginning: I congratulate you on your educational efforts. Even with the many online publishing tools, I still find it quite helpful to know that <b></b> gets you bold text and that an <a href> is a hypertext link, how you can include links to other pages on the Web.
The reason that sculpting (or channeling or carving) pagerank is complicated is because we have to define pagerank (more properly written as PageRank), explain how it’s calculated and why it’s simultaneously super important and almost irrelevant to Web site owners.
Back aeons ago — at least in Internet time — two Stanford grad students named Sergey Brin and Larry Page started thinking about how academic research papers used citations (we non-academics would call them references or footnotes) and how certain papers were cited far more often than others. What would happen if you could analyze all research papers in a particular area: would you be able to quickly identify the best, most influential papers? And if that was true, could you do the same thing with Web sites, simply analyzing which sites point to which other sites and then calculate the best sites by using this voting process?
The two grad students dabbled with the idea and, to cut a long story short, founded Google. After years of the Web continuing its aggressive, chaotic evolution their original insight into a page relevance formula still holds true and now has the name of PageRank, or Google PageRank.
To fully understand pagerank and how it can be channeled or sculpted, we need to add one additional concept: pagerank transference. The idea is that if you have a page with lots of pagerank that points to lots of other pages (let’s say 20) each link gets 1/20th the pagerank of the originating page. If the page has a pagerank of 100, each link would get a transferred pagerank “vote” of 100/20, or 5. If that same page had only two outbound links however, then each link would get 100/2 or 50 points.
Clearly, the more outbound links you have on a page, the less benefit each resultant destination page sees as the originating page gains in popularity. This is a bit confusing, but think about it this way: if we have a Web page with twenty outbound links (e.g., links pointing to other pages, either on our own site or another site) and our pagerank jumps from 100 to 200, each of those destination pages gains an additional vote of 5. Not so much. If we only have two outbound links, however, each sees a jump of 50 as our own page gains in pagerank!
The obvious question is whether you can control the flow of pagerank so that you can have outbound links that don’t get any votes?
You can. That’s what’s called the “nofollow” attribute and to see how it works we need to briefly sidetrack and talk about HTML. A hypertext link on a Web page has two elements: the destination URL and the text that’s to be shown as clickable. It looks like this:

In this instance, “http://www.google.com/” is the target address where you’ll be taken if you click on the words “visit scenic Google”. You already know this if you’re learning HTML, I’m sure.
To have a hypertext link not pass along pagerank, the secret is to add the nofollow attribute, actually a value to the “rel” (short for ‘relationship’) attribute. It ends up looking like this:

That’s the secret trick. Neat, eh?
I should note that those of us outside of Google know of PageRank as having a 0-10 score, where 10 is unbelievably rare. Anything above a PR4 is considered good, and PR7 and higher is great. I use a larger value in this column just to explain the concept.
And, finally, should you use these nofollow attributes to control how pagerank is distributed? Sure. It certainly makes sense that you might not care if some pages on your site ever show up in a search result, so why waste the “vote” on them? For example, sitemaps, legal notices, user agreements, etc.
Now you know.