Disambiguation pages, templates, navboxes, user pages, discussion pages, file pages, category pages, help pages, and Wikipedia policy/guideline pages (and everything else in "Wikipedia" namespace) are not articles (see WP:GOVP).
See Wikipedia:Article titles to learn how we title articles.
Each article has a scope, which is what the article covers. The article should contain a readable summary of everything within the scope, given due weight, based on what reliable sources say.
Articles range greatly in quality, from as high as featured articles to as low as candidates for speedy deletion. Some articles are quite lengthy and rich in content while others are shorter (possibly stubs) or of lesser quality.
"Articles" belong to the main namespace of Wikipedia pages (also called "article namespace" or simply "mainspace").