The Categories Block allows you to display a list of the Post’s Categories. Each Category is separated by a comma and will include a link to the individual Category Archive page. Although you can add this block into your normal Post content, it will be more useful adding it to your theme’s templates using the Full Site Editor.
Once you've added the block, there are further options available in the Settings Sidebar. You can change the Text and Background colours, and you can also change various Typography settings like Font size, Appearance, Decoration, Line height, Letter case & Letter spacing. Clicking on the Transform to Tags icon () allows you to switch this block with the Tags Block, which shows a list of the Post’s Tags.
Clicking on the Prefix and Suffix fields within the block allow you to add some extra text before and after the list of Categories.