Pages & namespaces
We call an article a page with content about a certain topic. An article is always sorted into the namespace "(Main)". These pages have no namespace prefix, like pages in other namespaces do ("Help:", "Templates:" etc.). Every article is on a page, but some pages have different content – see #Namespace for more information.
A page is every single page in TangoWiki. Every page has a unique URL. Pages include articles, discussion pages, special pages, template pages, category pages etc. Almost every page has an associated talk page to it, where questions about the content of a page can be asked.
A namespace is a group of pages. Every namespace has a prefix to its page title – with the only exception of the main space. So there is "Help:" for the help namespace and "Template:" for the template namespace. Some forms add a new page automatically into a namespace. The point of namespaces is to group certain pages and to distinguish between similar pages (like "Buenos Aires" for the city and "Song:Buenos Aires" for the Tango song.)
See more about namespaces in Help:Namespaces.
Categories are put into the end of the source code of a page and are shown at the end of a page. Categories allow simple sorting and linking of similar pages. When a page is sorted into a category, this category is created and on the category page itself all pages sorted into this category are automatically shown. The category page itself needs to be created like every other page (with text and categories) after this. More about categories. In the special pages there is a list of all categories.