When you look at the bottom of a Wikipedia article, you see category links. For example, the article Coat of arms of Copenhagen has the category links "1661 establishments in Denmark", "Culture in Copenhagen", "History of Copenhagen", "Danish coats of arms", "Municipal coats of arms in Denmark", and a bunch more category links for each symbol on the coat of arms. Category links are a big help for readers looking for articles related to a topic. Those links are there because editors like you added them. Wikipedia's software doesn't do automatic categorization, and Wikipedia employs no professional categorizers.
Adding categories to articles is easy: Just type a few words, add brackets, and publish these changes. The trick is figuring out what category links would provide maximum usefulness to readers, and that's what this chapter shows you. It also explains the other half of the categorization picture—the category pages where category links are listed. You can create and improve upon those pages, too.