what he means is that your content area needs to have a reapeating image so that it can expand with content or the size of the users screen. you would take a small slice of your content image, lets say a height of 5px and the width of how large you want it. It all depends on how it looks.
Then you would repeat the content
check out slicing web based images on google and you might get a few examples of how to do this. Let us know if you have anymore questions.
}/*just an example*/