Everyone uses different brow filling methods - some swear solely by pencils, while others prefer brow powders.
Don't feel the need to go run out and purchase a brow powder. Any matte brown eyeshadow similar to your hair colour will do. Although we all favour and thrive for eyeshadows with lots of pigment, we don't necessarily look for the same in our brow products because we want our brows to look to look natural. if you don't own an eyebrow pencil, you can use an eyeliner - but don't apply it straight on as it can look too intense for your brows. Scribble on the back of your hand, and run your brush through the product for a more natural look (or you can just lightly rub your brush across the tip of the pencil).
Try combining both because the pencil yields a very precise, clean line, whereas the brow powder gives a softer, more natural diffused line. The result is a very clean and precise brow, yet it's not as clean / chiseled as it would be if only a pencil was used.