By default, the more recently created articles are shown first. If "Reverse order" is selected under article configuration, then articles are shown in the order created. Up and down arrows in essence change what the system thinks is the order of creation.
Articles may be disabled and if so are visible only to those with permissions to create articles.
A limit can be set of how many articles to show on the main screen. When this limit is exceeded, a "See All Articles" link will appear that will take the visitor to archived articles.