Step 1

Open the image you want to add the fireworks to-- it should be a night shot with plenty of open sky. Open the firework image, select the Photoshop Move tool, and drag-and-drop the firework (click and hold on the firework, slide your cursor over the night image, and then release the mouse button). You can always select all of the firework (command/control-A), copy it (command/control-C), and then paste it into the night image (command/control-V) if you want, but I get a kick out of doing the drag-and-drop.