Take a Screenshot LG G3. 1  First, go to the screen that you want to capture an image of. 2  Press the volume down key and the Power key together at the same time.3  You have successfully captured the screenshot the screen will flash, and a Polaroid animation is displayed on the device with a shutter sound. Press the volume down key and the Power key together at the same time. 2  You have successfully captured the screenshot the screen will flash, and a Polaroid animation is displayed on the device with a shutter sound.