Alignment means, literally, how things line up. A composition that uses alignment to best effect controls how our eyes move across a text. Even if we're working with a text that is all words, every piece should be deliberately placed.
Alignment
News papers use alignment in order to organize all of their columns of text and their images. Alignment is defined as having something deliberately places and news papers follow this rule closely with how and where they place things. In this example the photo was aligned above the text in order to give a visual before what the viewer was going to read about.
Many websites such as this one use alignment in order to selectively decide where to place ads and other content they wish the viewer to see the most. For example they aligned the advertisements by other companies alone the top to be the first thing that catches the reader's eye.