An article is a page with some content which can be accessed from the menu on the website.
Click on the "Articles" link to open the article admin screen. Here you can view the current articles (if any), update/delete articles and create new article that you can link to a specific menu item link (that you created previously on the "Menu" admin screen). Please note the "Root" item link is always present, i.e it cannot be removed or edited, and the article linked to the root item link is the homepage which will be shown when viewing your website for the first time.