Photography is painting with light - you need light to make a photo, so in the purest sense what’s happening with fireworks is true photography. Long exposures and light… The camera will need to be steady, preferably supported by a tripod. You may get lucky without one, just lean your camera against a steady object, press the shutter and hold your breath. You are painting with light remember, so what if your light trails are a bit wobbly?
Choose a good spot, preferably with some foreground or water. Four to 15 seconds is a good starting point for shutter speed. Choose a depth of field of f/5.6 as a starting point, set focusing on manual, set white balance to daylight and your ISO to 100. Check your initial photos, and if they appear overexposed set the aperture to a higher humber (f/8 or f/11). If they appear underexposed, set the aperture to a lower number (f/3.5). A high ISO will make the sky appear grey, and we are after a black sky.
For you iPhone shooters out there, your options include a slow motion video, burst mode, or the Slow Shutter app. You will still need a tripod. The app gives you an immediate preview, so you can adjust. Use the Light Trails setting, put the ISO on Auto, and experiment.
This photographic website provides me the opportunity for self-expression, for sharing