Subpages can be useful for organizing and archiving project content, and for creating workspace under a user account. On a parent page, you can create a link to one of its subpages by typing [[/Name]]. If you end the link with a slash, e.g., [[/Name/]], the slashes are hidden in the output.
Articles don't have subpages. That is, subpages are not enabled in the article namespace, because many articles might qualify as subtopics of more than one topic. Instead, follow article naming conventions and include links to related subjects in the text.