WordPress makes it possible to pull in very specific types of content on your Web site through the <query_posts> template tag. If you place this template tag before The Loop (see Book VI), it lets you specify which category you want to pull information from. If you have a category called WordPress and you want to display the last three posts from that category — on your front page, in your blog sidebar, or somewhere else on your site — you can use this template tag.
The <query_posts> template tag has several parameters that let you display different types of content, such as posts in specific categories and content from specific pages/posts or dates in your blog archives. The <query_posts> tag lets you pass so many variables and parameters that we just can't list all the possibilities. Instead, you can visit this page in the WordPress Codex and read about the options available with this tag: http://codex.wordpress.org/Template_Tags/query_posts.
First, you have to find the ID number for the category you want to use; then you have to tell WordPress how to display the content by using the <query_posts> tag.
You can't easily find the unique ID number for a category unless you know where to look. To locate it, follow these steps:
The Categories page opens.