Wikipedia:Tip of the day/February 10, 2008
Let's say you have thought of a new category you want to place some articles in. To create this new category, go to one of the pages that you wish to put there, and add a category tag naming the new category to the end of the article, like this:
[[category:category name]]
...where in place of "category name" you type the actual name of the category. When you save the page, the category should appear on the bottom line of the page. If the page doesn't exist yet, it will turn up in red. But this doesn't mean there is no such category: it might exist but with a slight difference in naming. Before you create a new category, make sure it doesn't already exist. In a new browser window, click on "Special pages" in the toolbox menu on the left side of your screen. Then click on "All pages". Check the category namespace box, and then enter the name of the category. Look over the index for synonymous categories.
Once you have determined that the category does not exist, click on the redlink you created earlier, and then click on the article creation link provided in the instructions that appear on your screen.