@Gaston: Everyone starts somewhere :)
If it's any help, this is how the original author explained it:
.storycontent: The story content class. Change accordingly.
img: For images found inside the .storycontent posted story
460px: Change this accordingly (or lesser probably) to the width size of your story content box.
width: expression(this.width > 460 ? 460: true): max-width fix for IE.
This is my version: I'm not sure what theme you're using for your site, but most themes will enclose e.g. the post content in a box called a 'div'. There can be many, many divs as one box/div can fit into another.
Most people want to style their post content box, so they assign something called a 'class'.
In the example above, the class or style name is 'storycontent' as indicated by:
.storycontent img {
So if your div/box class name was 'postcontent', your first line would be:
.postcontent img{
You'll have noticed the img tag there: what this tag does is specify that this styling should only apply to images within the content box. This is because when you load an image file, <img src="link to image"> is used.
Then everything in the brackets { and } is just styling.
Just being a bit silly here: If we take some cupcakes (img) and box them up into two boxes (div) marked 'Cupcakes 1' (.postcontent) and 'Cupcakes 2' (.postcontent2) respectively, they could both have pink icing, or one might have blue and the other pink.
Not sure if this will help or confuse you even more ^^.
huotg01