Click the drop-down menu on the Layers pane to change the Blending Mode. Selecting “Screen” will turn the black background invisible. Don’t worry if there are visible traces left, we’ll address that shortly.
While holding down the Ctrl key, click and drag the muzzle flash layer to where it belongs.
You can resize the muzzle flash layer by going to Edit>Transform>Scale, then dragging a corner of the bounding box to make it larger or smaller. Holding the Shift key while doing this will maintain the layer’s aspect ratio.
You can also tweak the layer brightness by going to Image>Adjustments>Brightness/Contrast.
Use the sliders to make adjustments. Increasing the Contrast will get rid of any visible remnants of the black background.
Muzzle flash is done! It looks much better with the added FX, but if you’re like me you’ll want to add a little extra something. Read on!