The VDG started out as the Visual Design Group, but has grown into a team dedicated to the whole user experience, including what is often called human interface design. The aim is to help KDE create software (and websites and promotional material) that is both beautiful and a pleasure to use.
You don't need to be a talented artist or an experienced interface designer to contribute to the VDG (although, of course, we are always looking for people with those skills). If you have ideas about how software should look and behave, you are a designer too, and we'd love you to join in.
The main place the VDG discusses things is on the forums. Sign up for the forums if you haven't already, read through the "sticky" posts (at the top) and dive in.