If you read this page in a web browser, you should see standard red text in a sans-serif font, and two copies of the Freeola forums header banner, plus a navigational list of links.
If you print it, or use print preview, you should see black text with a serif font, which is set to justify, a little bigger, and no images or navigational list.
The text won’t span the whole page, as the CSS property width has been inherited by the printer version, because the media attribute hasn’t been used on the first style declaration.
The CSS value justify is an alignment property, and is used to make the text align to both the left and right margin of a page.