You can make your blog more structured and easy to navigate by categorizing your posts.
Creating a new category
To create a new category, go to the Manage menu, then select the Categories section.
Change the category of a post
To change a posting from one category to another, go to the Manage menu -> then select Posts and click Edit. From the menu to the right choose the desired category.
Delete a category
Note that deleting a category does not delete posts from that category. It will just set them back to the default category Uncategorized.
For more help with visual demo go to the WordPress Tutorial provided.