You can check out the Technorati WordPress tag page, for starters.
Now the way it works is you “tag” posts in your weblog so it appears in the right technorati tag page. If you assign a post to a category, then the post is tagged as belonging to a tag that is the same as the category. So in other words categories are automatic tags. But if you want to tag specific post, then you could use the TechnoTag Plugin to make life simpler.