This is how your eight-point garbage matte will start out. You'll want to move the 8 points to block out the unwanted parts of the background. For each point, click the plus sign to the left of the numeric coordinates, then move to the canvas, and click where you want that point to be. If you miss the mark, you'll have to go back and click the plus sign, again, before reselecting the point in the canvas. Go to the next page, to see how I defined my garbage matte.