Tonight I went to the Seattle Weblogger Meetup to talk with folks about tagging and how they do it. Tagging is inserting special HTML into your blog to bring keywords to the attention of a site like Technorati. People can then use Technorati search to find blogs (including yours) that have called a particular keyword.
I guess what had been puzzling, and perhaps irritating, me about tagging is that it seems like an overlap with Google. You publish a blog entry, Google spiders (reads) it, and then anyone looking for particular words, phrases, or word combinations can find them via a Google search if you've used them in your blog.
What I learned tonight from Daniel Talsky and Bre is that there are some significant differences. Bottom line: If you want more hits on your blog, you need to tag your entries. Technorati is not the only tagging system; the other major one is del.icio.us.
Here's a page that explains the technical aspects of tagging using Technorati. Also, Technorati now allows people who create a (free) Technorati account to tag an entire blog by listing keywords that relate to the blog itself, rather than to a specific entry.