Using Query String to Maximize Code Reuse

Ok, i’ve read a tutorial about passing variables to HTML. But this tutorial isnt clear for me…

EXAMPLE 1
Using Query String to Maximize Code Reuse

I really dont have an idea what to do inside flash, bec the author only said:

Assuming the image filename is image1.jpg, located at a folder named images. And assuming that the Flash movie will use a variable named imageFilename to refer to the file, then we can do this

How do I do that? Like having a empty movie clip and giving an instance name of imageFilename?

Pls help. TT_____TT

Im at my wits end… Thank you in advance.