A browser window is a main window of Diary++X.
There are category list (article group, bookmarks, history) and calendar on the left side of the window. There are article list and article view on the right side of the window.
When you select one or more categories in the category list, you can view articles contained by the categories at the article list.
To show an article at the article view, you should select one article from the article list.
You can use tabs to manage multiple article views.