Each Refined Site has its own structure. The structure is built using Categories and Jira projects. Each category and Jira project have their own landing page that can be modified.
...
Categories are added to sites with two purposes:
A landing page for the category where you can put content from different sources.
A structure that ease navigation on the site.
Categories are added to a specific site, and can be dragged-and-dropped between sites.
Refined sites work a bit differently, based on the applications you work with in Jira: Jira Service Management, Jira Core, and Jira Software.
Adding a Category
Open the Site Builder and click the click the + in the top right corner of a site block.
...