Help:Categories
Categories group related pages. Follow Project:Categorization and inspect existing categories before creating a new one.
Add a page to a category
Place a category tag near the end of the article:
[[Category:Ships]]
Use an existing, relevant category. A category name is a page title, so spelling matters. Prefer an appropriate specific category instead of adding every parent in its hierarchy.
Link without categorising
Start the link with a colon:
[[:Category:Ships|ship categories]]
Without that colon, the tag adds the current page to the category rather than creating an ordinary link. This distinction matters in templates and documentation.
Sorting and templates
A sort key changes where a page appears in a category:
[[Category:Ships|Example sort key]]
Do not add arbitrary keys where the page title already sorts correctly. A template can add categories to pages that use it. Keep template-only categories out of transcluded article content, and test before changing a widely used template. See Help:Template. Discuss a category merge or rename through Project:Categories for discussion.