The Joomla! Articles Assignment gives the ability to select one or more Joomla! Articles which will be accompanied by your box. This means that when the visitor reads specifically that (or those) Article(s) then the box will be displayed to him.
In the table below you can see which options are available to setup the Joomla Articles Assignment.
Click in the textfield so a selectbox pops up from which you can filter the Joomla! Articles that you'd like by typing on the fly.
Once you select one you can continue typing to find the next one and so forth.
The most common use case for the Joomla! Articles assignment is when the box you are about to display is directly related to that specific article. For instance, say that your article is about the daylight savings time subject, then an appropriate box for this article would be one containing a poll for whether the visitor agrees to have daylight savings time adjustment or not.
It's important to remember that you will be able to choose only from the articles which are currently published.