Shortcode is a plugin that adds several useful shortcodes that you can use in your blog posts and pages.
/wp-content/plugins/directory of your WordPress installation
Using the plugin is as simple as adding any of the shortcodes found at http://www.maxpagels.com/shortcodes.txt to your blog posts and/or pages (to make sure that the shortcodes are properly identified, use WordPress's HTML editor instead of the visual editor).
Some of the codes you can use include:
[postcount]: the total number of published blog posts
[catcount]: the total number of categories (those that contain one or more posts)
[tabcount]: the total number of tags (those that contain one or more posts)
[ageindays]: the number of days since the first blog post was published
When you are done inserting the shortcodes you want to use, save the changes to your posts and/or pages and things should start working straight away.