It is formulated to add volume, fill in sparse areas, and create a natural-looking brow shape. The Brow Fiber Filler typically comes in a pencil-like format with a spoolie brush at one end. The product itself is infused with fibers that adhere to the brow hairs, helping to create the appearance of fuller and more defined eyebrows. The shade "Dark Brown" indicates that the Brow Fiber Filler offers a rich, deep brown color that is suitable for those with darker hair. To use the Revlon Brow Fiber Filler, you would typically start by brushing your eyebrow hairs into place using the spoolie brush. Then, using the pencil end, you can fill in any sparse areas or gaps in your eyebrows, following the natural shape of your brows.