They hold organized data and have integrations and views for those data. It's nothing fancy like a mature sql-database-system, but you have different high-level views you can configure through the interface. So you can make tables with filters, a kanban, calendar, timeline and some more[1]. People use it for task-lists, project-management, to manage their movie and book-lists, etc.

[1] https://www.notion.so/de-de/help/guides/when-to-use-each-typ...