In the category management you administer the category structure of your shop. In Shopware 6, categories are also used to organise the shop pages and the service menu and to create landing pages.
You can find the module under Catalogues > Categories.
ThemeWare® tip: ThemeWare® enhances your listing pages – for example with subcategories in the listing, highlighted categories and flexible product box layouts.
Further information
Please find more information regarding "Categories" in the official Shopware documentation:
Shopware documentation: Categories