Sandpapers are essential to creating a smooth surface on which to apply finish. Usage information is here.
Silicon Carbide Sandpaper
Silicone carbide sandpaper is often a dark gray or black color and usually can be used either web or dry. Use it on acrylics wet and on woods dry. This type of sandpaper is used for sanding automobile finishes, and is available in grits up to 2000. It can be used wet or dry and can be washed off and re-used.
Aluminum Oxide Sandpaper
This is the most common form of sandpaper known to all woodworkers. It is usually a light brown or beige color. It is often coated with a stearate compound to prevent the sanding dust from sticking to the sandpaper. The compound may interfere with some finishes. It always has a paper backing and must be used dry.