Sunroof deflector (B3)

It's very easy. They usually have two brackets that just hook onto the sunroof opening.

I generally like mine ('91 GTI) however do note that no matter how clean you keep your car, the deflector will manage to trap dust between the rubber lip and the roof and over time you will get scratches and eventually it'll wear through the paint. If I had to do it all over again, I wouldn't.