When outputting a single article, you can simply define what article you want to place data from. You can do this by using the title, alias or id of the article:

{article title="Fox Terrier"}...{/article}
{article alias="fox-terrier"}...{/article}
{article id="123"}...{/article}

When inserting the {article} using the id attribute, you can also add a comment (eg. the Title) after the ID with the following syntax. For example: 

{article id="123#My Fox Terrier article"}...{/article}

This last syntax, unlike when using just the title attribute, won't bind the article to always keep the same title, because the syntax will still only depend on the ID. However, this allows you to add a comment to remember what the article is about when you insert it.

Current Article

You can also make the tag use the current active article.

This can be useful when you want to place data from the current article inside the article itself, or inside a module.
To do this, simply don't give the article tag a specific article: