You need to unscrew the knee pads and use the holes to secure the skirt near the steering column. You may find you need longer screws. There should be 2 hooks that then attach down by the front wheel well to finish securing the front.
There should be a bib that you can put around your neck, strap my be in a zipper pocket. There should also be a waist strap.
I've had 2 different models but the attachments were basically the same. Good luck! I both love and hate them. I have waterproof cold weather over pants I've been using the last few seasons however the skirts are obviously quicker. May want to put protective peel away clear film where it rubs against the frame if that is a concern.
Here is a couple of pics from my old GTV.