Creating subpages on a MediaWiki wiki is simply a matter of adding the subpage name after the main page name and a slash. For example, if you have "User talk:1442670" (the talk page for your wiki account, Lord G), creating the page "User talk:1442670/Game rules debate" would be a subpage of your talk page. Whether subpages produce breadcrumbs at the top of the page ("< User talk:Lord G." at the top of the "Game rules debate" subpage) is a matter of PHP code on the server, but I believe the User Talk namespace is among the namespaces that handle subpages by default. Edit: Yep, User talk namespace has subpages enabled by default: <a href="https://www.mediawiki.org/wiki/Manual:$wgNamespacesWithSubpages#Default_value" rel="nofollow">https://www.mediawiki.org/wiki/Manual:$wgNamespacesWithSubpages#Default_value</a> The Template namespace doesn't, which is annoying for me when trying to document templates. I had to do some hacking with the {{documentation subpage}} template code to get it to display properly without {{SUBPAGENAME}} working on a template subpage.