Whenever you're on an article page, no matter the website, just click the Readable bookmarklet; a reformatted version of the article will appear on top of the original page.
"What's an article page?", you ask; good question. An article page is any page that contains one large block of text — like, for example, all newspaper articles. Readable is only designed to automatically process these kinds of pages.
On any other type of page, you can still take advantage of Readable, but in manual mode: simply select the text you would like Readable to display, and then click the bookmarklet.
When you're done reading, double-click the background to dismiss the Readable overlay.
Readable -- what Readability was before it became something else.