The Article list is a list of articles that contained by the selected category, results of searching articles or clicking a date on calendar.
You can select an article to view at article view and can select multiple articles to specify for command "Print Selected Articles" etc.
To show articles contained by an category, select the category at the categories list. When you want to retrieve diary of 2009, for example, select category 2009, Diary++X shows the list of diary April 2009 when you select category 2009 > April 2009.