Dark Transfer is best for dark-colored fabric/shirt and has an outline same with the color of the fabric/shirt.
On the other hand, when using a dark transfer paper, the image is now printed on the positive side, simply put; you print your image like you would normally do. After having printed the image, the coating that comes with the paper will be peeled off and is placed directly on the surface where you want it imprinted, your design should be facing you, as you set it on your heat press, with the parchment paper sheet over it.