Topic on Forum:Trope Talk
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Launching a category is easy - add it to one of the pages that you want listed in the category. That will create a redlink that you can click on and edit the page.
The boilerplate dropdown has "Category page" as an option, near the end - select that before you type anything into the edit box and you'll get the minimum that you need for a category page. You can delete the {{main|{{PAGENAME}}}} text since this won't be a category for an existing trope or work page.
Once you've saved off the new category, it's just a matter of adding it to other pages.