Use the thick, rounded-cut brush to apply the middle shade over the entire brow. You can mix it with the other two shades to adjust the color to your preference.
Use the thin, angled-cut brush to apply the darkest shade in line-like strokes at the brow tail and areas without brow hair.
Pick up the lightest shade with the thick, rounded-cut brush to blend and adjust the color at the front of the brows, or apply along the bridge of the nose for contouring.