Now I only Jumped on a pose stand to photograph these steps. Applying nails textures does not require this. Heres my High Feet in a pair of boots with the silver nailpolish that you can use from the polish HUD that comes with your feet.
Now make sure you unpacked your HUD from your purchase, and navigate to the folder in your SL inventory to where the mani/pedi HUD's are located.I recommend you right click and hit ADD. Your Nail Pedicure HUD should popup in the center of your screen. (Yes you can resize the HUD if its to big)
It's pretty simple really. You get a choice of colors most times. Just click the color you want and it should automatically apply to the nails. I chose Dark Purple as it matches the makeup I am wearing at the moment.
Now detach your HUD by right-clicking on it and choosing DETACH. And your done. Its basically the same for fingernails using the Manicure HUD with your SLink hands or nails.